CN1287080C - Piston for internal combustion engine and method of manufacturing the same - Google Patents

Abstract

A forged piston for an internal combustion engine formed from an aluminum alloy containing silicon in an amount of 6 to 25 mass%, includes an oil ring groove section (12) and a skirt section (13). The ratio (A/B) of the average size (A) of eutection silicon grains contained in the oil ring groove section to the average size (B) of eutection silicon grains contained in the frontal end portion (18) of the skirt section is at least 1.5. The average size (A) is at least 4 [micro]m. With the configuration such that the average size (B) is small and that the average size (A) is large, the skirt section exhibits excellent forgeability and the oil ring groove section exhibits reliable mechanical workability and improved wear resistance.

Description

The forging piston and the manufacture method thereof that are used for explosive motor

The cross reference of related application

The present invention requires in the applying date rights and interests of the provisional application No.60/308110 of submission on July 30 calendar year 2001 according to 35U.S.C. § 119 (e) (1).

Technical field

The present invention relates to a kind of forging piston of making by silumin that is used for explosive motor, and relate to a kind of method that is used to make this piston.

Background technique

Usually, the piston that is used for explosive motor by metal (forever) mold casting (permanent mold casting) production.At first, thus molten aluminium alloy is poured into a mould in the mold this aluminum dipping form is made a piston prefabricated component.Then, the prefabricated component of this formation is carried out required heat treatment, for example, artificial aging (intentional aging) is handled, thereby and carries out required machining then to produce a finished product.

Recently, in some cases, produce the explosive motor piston by forging.The fusion aluminium-silicon alloys is cast continuously, thereby extrude and use blank to form one; This blank is heat-treated (homogenization processing) to obtain owing to the segregation of solute element or the even distribution of the internal stress that contraction produces during curing; And form a minor diameter pole by extruding the blank that makes this formation.Alternatively, the fusion aluminium-silicon alloys is cast continuously, thereby to form a minor diameter continuous casting rod; Casting rod to this formation carries out the homogenization processing; And this rod carried out cutting to form the minor diameter pole.The minor diameter pole that so forms is cut into as forged material to be processed.This forged material is preheated, use a warm forming machine to forge into a piston prefabricated component then.Then, this prefabricated component is heat-treated, for example, artificial aging is handled, thereby and carries out machining then to produce a finished product (that is a piston).According to the use of piston, in order to improve wearability and heat resistance, the head of this piston or the part of the piston side wall between last compression ring and head can stand alumite/alumina layer processing or coating forms processing.

Recently, require day by day to improve to be used for for example fuel economy of the explosive motor of automobile.In order to satisfy this requirement, attempted reducing the weight of car body, and developed the lightweight motor.For example, be used for the piston of motor, and developed the thin-walled piston with aluminium production.

Simultaneously, require to satisfy the high-quality piston of the requirement of high-performance enginer day by day.

When producing a piston, because the technical limitation on this casting method is difficult to reduce skirt section thickness by traditional metal (forever) mold casting method.Therefore, usually, thereby this cast pistons is carried out cutting to reduce the thickness in this skirt section.When by Foundry Production one piston, the structure of this piston is owing to the low solidification rate during casting becomes thicker, and therefore the piston that is obtained has good machinability.Yet, since bigger by the thickness and the dimensional changes of casting the piston space that forms, so be difficult to control the dimensional accuracy of final products.In addition, subsurface defect in the piston that forms by casting, may occur, thereby reduce its intensity as hole, micro hole.Therefore in order to improve piston intensity, the whole wall of this piston is thickeied, and the increase of the thickness of its strengthening rib, thereby makes the piston that forms by casting be unsuitable for using in high-performance enginer.And, because the thickening of piston wall causes the performance variation of piston space to become big.As from the foregoing, produce motor and require further improvement piston with unfailing performance.

Simultaneously, when by forging when producing a piston by a forged material, because this forged material does not comprise subsurface defect basically, and this forged material has reliable mechanical property, becomes even so constitute the thickness of the section/part of this piston.Therefore can produce piston by forging with reliable quality.But, although this forged material is suitable for forging thin, a long part, a skirt section for example, because this forged material has thinner structure, the machinability of this material is satisfactory inadequately.For example because produce the chip rather than the part of conitnuous forms during machining, the manageability of chip (manageability) suffers damage, and causes lower productivity.In addition, the surface roughness of the oil ring groove of the final piston product after machining part is also unsatisfactory.When using continuous casting, because the crack appears in the curing shrinkage internal stress that is produced in the ingot casting, the component of alloy to be produced is applied restriction when casting in order to prevent.Therefore can not easily produce as one can provide a kind of as have higher-strength, than the alloy of component forged material, that have hope of the piston of high abrasion resistance and at high temperature high intensity than required intensity.

As from the foregoing, the present invention has developed and its purpose is, a kind of forging piston that is used for explosive motor is provided, this piston comprises: one has the machinability (for example at the oil ring groove that has reliable dimensional accuracy aspect surface roughness and the planeness) of improvement, one (for example has good mechanical property, constitute the head surface of this head and wrist pin part and at high temperature have good mechanical strength property) head, one skirt section and with good forgeability has the oil ring groove part of reliable wearability.

Summary of the invention

The invention provides a kind of is the forging piston that is used for explosive motor that the aluminum alloy of the silicon of 6-25% is made by comprising mass ratio, this piston comprises an oil ring groove part and a skirt section, the ratio (A/B) of the average-size (B) of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the average-size (A) that wherein is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in this oil ring groove part and the fore-end that is included in this skirt section is at least 1.5, and this average-size (A) is at least 4 μ m.

This forging piston comprise the ratio (C/D) of the average-size (D) of the primary silicon crystal crystal grain in a kind of average-size (C) that wherein is included in the primary silicon crystal crystal grain in the oil ring groove part and the fore-end that is included in the skirt section be at least 1.3 and this average-size (C) be at least the forging piston of 15 μ m.

Forge in the piston at every kind, it is the Mg of 0.1-2% that aluminum alloy comprises Cu and the mass ratio that mass ratio is 0.3-7%.

Any aluminum alloy can comprise the Ni that mass ratio is 0.1-2.5%.

The present invention also provides the method for the forging piston that a kind of manufacturing is used for explosive motor, comprises the steps:

To comprising mass ratio is that the molten aluminium alloy of the silicon of 6-25% carries out unidirectional curing casting to produce an ingot casting as the forged material with each other relative first surface and second surface thus, and the average-size that wherein is included in the silicon crystal grain in the first surface is different from the average-size that is included in the silicon crystal grain in the second surface;

This forged material is preheated;

This forged material is placed a forging die, and the surface corresponding to piston crown of this mould is faced on the feasible surface that comprises the silicon crystal grain of big average-size, thus this forged material is forged into a piston prefabricated component;

This piston prefabricated component is carried out artificial aging to be handled; With

Piston prefabricated component to this formation carries out machining, to make a forging piston that is used for explosive motor thus.

In this manufacture method, unidirectional curing casting be included as the average-size (A) that obtains to be at least the Eutectic Silicon in Al-Si Cast Alloys crystal grain in 1.5 the top that is included in ingot casting be included in this ingot casting near the ratio (A/B) of the average-size (B) of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the part of a cooling plate and be at least the average-size (A) of 4.0 μ m and the cooling carried out.

In this manufacture method, unidirectional curing casting comprises: for obtain be 0.85 or littler, from the downward 5mm in top that solidifies mould and from the sidewall of curing mold inwards the measured cooling rate (E) of the some e of 5mm with make progress 1mm and from the cooling carried out of the ratio (E/F) of the cooling rate (F) measured of the some f of 5mm inwards of the sidewall of curing mold, wherein cooling rate (E) is at least 0.5 ℃/second in bottom from curing mold.

In any manufacture method, with one be in 350 ℃ to from the solidus temperature of aluminum alloy (℃) temperature that deducts in the scope between the difference of 10 ℃ of gained preheats.

As mentioned above, according to the present invention, can produce a kind of forging piston that is used for explosive motor that comprises an oil ring groove part and a skirt section, the average-size that wherein is included in eutectic in the fore-end in skirt section and primary silicon crystal grain is less, and it is bigger to be included in the average-size of eutectic in the oil ring groove part and primary silicon crystal grain.Because this configuration, this skirt section has the identical good forgeability in skirt section of the piston that becomes with continuous casting clavate by a minor diameter, and so can reduce the thickness in this skirt section.In addition, the oil ring groove part has the identical good chip manageability of oil ring groove part with the piston that forms by casting during milling, and this oil ring groove has less surface roughness and has good wearability.

Description of drawings

Fig. 1 (a) is a schematically illustrated embodiment according to the forging piston that is used for an explosive motor of the present invention vertical sectional view, and it comprises the sectional drawing in a skirt section;

Fig. 1 (b) is the vertical sectional view of the forging piston of a schematically illustrated Fig. 1 (a), and it comprises the sectional drawing of a piston pin hole;

Fig. 2 one is used for the schematic representation of an example of the foundry equipment of unidirectional curing casting;

Fig. 3 one illustrates the explanatory of the point in the mould that is arranged on a unidirectional curing apparatus, wherein in these point measurement cooling rates;

Fig. 4 (a) one is used for the side view of the Compax milling cutter of milling test;

Fig. 4 (b) is the plan view of cutter among Fig. 4 (a);

Fig. 4 (c) is the front elevation of cutter among Fig. 4 (a);

Fig. 5 one is illustrated in the explanatory view of an applied forging equipment when making forging piston of the present invention.

Embodiment

The following describes the embodiment of explosive motor according to the present invention with the forging piston.

Explosive motor of the present invention comprises that with the forging piston one has the head surface of valve pit, the skirt section of a big thickness, a strengthening rib, an oil ring groove part and a piston pin hole.

Fig. 1 illustrates an embodiment's of the forging piston that is used for explosive motor of the present invention sectional view.Fig. 1 (a) is the vertical sectional view of this forging piston, and it comprises the sectional drawing in a skirt section 13.Fig. 1 (b) is the vertical sectional view of this forging piston, and it comprises that one has wherein inserted the sectional drawing of piston pin hole 14 that is used for this piston is connected to the wrist pin of a connecting rod.The upper surface of this piston is one to have the head surface 11 of valve pit.Oil ring groove 12 is as the groove that cooperates with piston ring.This oil ring groove is necessary along the direction vertical with the perisporium of this piston, that is, and and along the direction setting vertical with vertical direction.This skirt section 13 is used for making piston to remain on the guiding element of the position of cylinder body lining as one, and need have high strength and high abrasion resistance.In order to reduce the weight of piston, require this skirt section to have a thickness that reduces.The profile of one piston prefabricated component (i.e. a forging product) is labeled as 15 double dot dash line with one and draws.One is labeled as 16 solid line through the profile of mach piston final products with one draws.Mark 17 expressions one strengthening rib, the front end in mark 18 these skirt sections 13 of expression.The height of the front end in this skirt section that begins to measure from the bottom of this piston is 40% of the overall height of this piston.Because when forging, sizable plastic flow occurs, require this front end to have good forgeability at this front end.

Explosive motor of the present invention is that the aluminum alloy of the silicon of 6-25% is made with forging piston by a kind of mass ratio that comprises.The ratio (A/B) of the average-size (B) of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the average-size (A) that the characteristics of this forging piston are to be included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part 12 and the fore-end 18 that is included in this skirt section 13 is at least 1.5 (being preferably at least 1.6), and this average-size (A) is at least 4 μ m, is preferably at least 4.5 μ m.

Under the situation of average-size (A) less than 4 μ m, when oil ring groove partly stood milling, the chuck of a milling cutter and a milling machine tended to and longilineal chip tangle up.And the chip of tangle up can scratch the surface of the piston for the treatment of milling.In addition, talus accumulation and form a thin filiform in the bottom of this milling machine and pile and covered whole chuck up to this chip so that this milling machine can not work again, thereby causes lower productivity.The forging piston that use is tied with the milling machine milling of chip has bigger surface roughness, this means that the quality of this forging piston can not be satisfactory.

Because oil ring groove part 12 circumferentially is continuous along the whole of this piston, the elongated shape chip that is produced needs self fracture.Thereby, need good chip manageability.

With forging in the piston, the average-size that is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part is at least 4 μ m at explosive motor of the present invention.Therefore, when this oil ring groove was partly carried out machining, the chip that is produced can easily fragment into little chip owing to silicon crystal.Therefore, can prevent that chip is entangled in milling cutter or the chuck.In addition, owing to can prevent the accumulation of the filament shape chip in milling machine, so improved the manageability of this chip widely.And, owing to can prevent that chip is wrapped in the milling cutter or just in the product of milling, therefore the product that is milled into has a stable surface roughness.

Be at least 4 μ m because be included in the average-size (A) of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part, this oil ring groove partly has good wearability.Because the upper and lower surface and a piston ring friction of this oil ring groove when motor moves, so this oil ring groove part must have high abrasion resistance.Piston crown surface (that is, one is exposed to the surface of the firing chamber of this motor) is by the high-temperature combustion gas heating that is produced during fuel combustion, and near the temperature this piston crown raises.Compare with the skirt section, be arranged near this piston crown oil ring groove part and that contact with an engine cylinder inwall and more working under the exacting terms.Therefore, this oil ring groove part must have good wearability.When this average-size (A) during less than 4 μ m, it is not enough that the wearability of this part becomes.

At the forging piston that is used for explosive motor of the present invention, the average-size that is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part is at least 4 μ m.Therefore, this oil ring groove partly has enough wearabilitys, and need not be near any processing of carrying out this oil ring groove in a high-performance enginer, being carried out that is used to improve wearability, for example hard alumina layer (hard-alumite) is handled or is used the coating of an abrasion-resistant coatings agent to handle.Therefore, in the present invention,, can reduce the cost of each piston, thereby a cheap motor can be provided owing to do not need this expensive processing.

The ratio (A/B) of the average-size (B) of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the average-size (A) that is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part and the fore-end that is included in this skirt section is preferably at least 1.5, more preferably is at least 1.6.In other words, average-size (B) is less than average-size (A), and average-size (B) is 0.67 times of average-size (A) or littler, and reason is as described below.

Skirt section 13 is not continuous along the whole periphery of this piston, and by the wrist pin section of being divided into partly.Therefore, when in machining process, along the circumferential direction milling is carried out in this skirt section, the milling in skirt section is become discontinuous, and therefore can prevent that chip is wrapped in the milling cutter.Therefore, be 0.67 times of average-size (A) or littler as long as be included in the average-size (B) of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the fore-end 18 in this skirt section, just can obtain the chip manageability of the satisfaction when machining.

On the contrary, when average-size (B) surpasses 0.67 times of average-size (A), though keep the wearability of oil ring groove, the plastic flow in the good skirt section that during heat forged, may just can not obtain.For example, following problem may occur: although kept the good plasticity workability in this skirt section, the wearability of this oil ring groove part suffers damage; Perhaps, although this oil ring groove partly has good wearability, the plasticity workability in this skirt section suffers damage.As a result, become and be difficult to provide the piston that comprises oil ring groove part and have the skirt section of excellent plasticity processability with good wearability.

Yet at the forging piston that is used for explosive motor of the present invention, the average-size (B) that is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the fore-end in this skirt section is included in 0.67 times of average-size (A) of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part or littler.Therefore, even when the thickness in this skirt section reduces, can not produce the crack in the front end in this skirt section in being positioned over a forging mould, and the plastic fluidity of this front end in this forging mould can not suffer damage yet yet.Therefore, owing to can reduce the thickness in this skirt section, so can easily reduce the weight of this piston.Because the skirt section that thickness reduces can reduce by forging formation and because of the required machining allowance of machining, so can improve productivity and output based on the piston of (necessarily) material.

Be the forging piston that is used for explosive motor of the present invention that the aluminum alloy of the silicon of 6-25% is made by a kind of mass ratio that preferably comprises, the ratio (A/B) of the average-size (B) of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the average-size (A) that is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part and the fore-end that is included in this skirt section is at least 1.5, and this average-size (A) is at least 4 μ m, the ratio (C/D) of the average-size (D) of the primary silicon crystal crystal grain in the average-size (C) that is included in the primary silicon crystal crystal grain in the oil ring groove part and the fore-end that is included in this skirt section is at least 1.3, and average-size (C) is at least 15 μ m.

With ratio (A/B) be set to be at least 1.5 and average-size (A) be set to be at least 4 μ m reason as mentioned above.

In some cases, comprising mass ratio is that the aluminum alloy of the silicon of 6-25% has a wherein primary silicon crystal crystal grain according to the cooling rate of this alloy and is scattered in structure in the Eutectic Silicon in Al-Si Cast Alloys structure.

In this case, the average-size (C) that is included in the primary silicon crystal crystal grain in the oil ring groove part preferably is at least 15 μ m, more preferably is at least 17 μ m.This can further improve the machinability and the wearability of oil ring groove part.Yet,, just can not obtain the effect of this primary silicon crystal crystal grain fully when this average-size (C) during less than 15 μ m.

With forging in the piston, the average-size (A) that is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part is at least 4 μ m at explosive motor of the present invention, and the average-size (C) that is included in the primary silicon crystal crystal grain in this part is at least 15 μ m.Therefore, when this oil ring groove partly stood machining, the chip that is produced can easily fragment into little chip owing to silicon crystal.Therefore, can prevent that chip is wrapped in milling cutter or the chuck.In addition, owing to can prevent the accumulation of the filament shape chip in milling machine, so improved the manageability of this chip widely.And, owing to can prevent that chip is wrapped in the milling cutter or just in the product of milling, therefore the product that is milled into has a reliable surface roughness.Be at least 15 μ m because be included in the average-size (C) of the primary silicon crystal crystal grain in the oil ring groove part, this oil ring groove partly has the wearability of improvement.

The ratio (C/D) of the average-size (D) of the primary silicon crystal crystal grain in the average-size (C) that is included in the primary silicon crystal crystal grain in the oil ring groove part and the fore-end that is included in this skirt section preferably is at least 1.3, more preferably be at least 1.4, reason is as described below.When ratio (C/D) when being at least 1.3, can improve the wearability and the machinability of this oil ring groove part further, and can keep the plastic fluidity of the fore-end in this skirt section.On the contrary, when this ratio (C/D) less than 1.3 the time, the wearability and the machinability of this oil ring groove part suffer damage, perhaps the plastic fluidity of the fore-end in this skirt section suffers damage.

Preferably, also to comprise mass ratio be the Cu of 0.3-7% (more preferably mass ratio is 0.4-6.5%) to the aluminum alloy that is used to form this piston and contain the Mg that mass ratio is 0.1-2% (more preferably mass ratio is 0.15-1.8%).Add these alloying elements and strengthened the hardness of piston and the mechanical strength property that comprises tensile strength, 0.2% yield strength and fatigue resistance of piston.In addition, because can produce the piston of this thin walled structures, can reduce the weight of this piston.When the amount of alloying element drops to lower limit when following, then can not obtain the effect of these elements.On the contrary, when the amount of alloying element surpasses CLV ceiling limit value, can not reentry and the additional suitable effect of amount of element, and cost of material increases, and the forgeability of piston suffers damage.

Preferably, the aluminum alloy that is used to form this piston also comprises the Ni that mass ratio is 0.1-2.5% (more preferably mass ratio is 0.2-2.0%), and reason is as described below.Adding Ni can strengthen piston intensity at high temperature and raising is arranged near this piston crown and the serviceability of the oil ring groove that contacts with an engine cylinder-body inwall under the engine operating condition of harshness part.When the amount of Ni drops to lower limit when following, then can not obtain the effect of Ni, and when the amount of Ni surpasses CLV ceiling limit value, the suitable effect of amount with additional Ni can not reentried.In addition, when the amount of Ni increased, because Ni is a kind of element of costliness, cost of production increased.

The following describes an a kind of embodiment who is used to forge the manufacture method of piston of the present invention.

Manufacture method of the present invention may further comprise the steps: thus be that the molten aluminium alloy of the silicon of 6-25% carries out unidirectional curing casting to produce an ingot casting as the forged material with each other relative first surface and second surface to comprising mass ratio, and the average-size that wherein is included in the silicon crystal grain in the first surface is different from the average-size that is included in the silicon crystal grain in the second surface; This forged material is placed a forging die, and the surface corresponding to piston crown of this mould is faced on the feasible surface that comprises the silicon crystal grain of big average-size, thus this forged material is forged into a piston prefabricated component; This piston prefabricated component is carried out artificial aging to be handled; And the piston prefabricated component of this formation carried out machining.

Piston by this method manufacturing of the present invention has above-mentioned feature.

To describe this manufacture method in detail below.

Forged material is to obtain as raw-material aluminum alloy by unidirectional curing casting is a kind of.This manufacture method has for example been used disclosed and foundry equipment shown in figure 2 in JP-A HEI 9-174198.

In Fig. 2, label 201 expressions one cooling plate.On this cooling plate 201, be provided with a main mould 202.On this main mould 202, be provided with a container 203 that is used to admit the molten aluminium alloy of supplying with by a for example smelting furnace (not shown) 207.As shown in Figure 2, the bottom of container 203 is as the top of mould 202.This container 203 is communicated with main mould 202 by a molten metal inlet 204.One obstruction piece 205 is arranged on this inlet 204.By promoting this obstruction piece and molten alloy is injected this mould by an equipment (not shown) that is used for this obstruction piece of vertical movement, the height/liquid level of the molten alloy of injection moves up.After the injection of finishing molten alloy, perhaps after, thereby this obstruction piece is moved down to stop the injection of molten alloy through a preset time section.Reference number 208 expression one lid, and mark 209 expressions one are used to make molten alloy to remain on electric furnace under the predetermined temperature.On it, spray water to wait and cool off this cooling plate 201 by being arranged on nozzle 210 below the cooling plate by one.Label 211 and 212 is represented a shell chamber and a drain outlet respectively.

Be injected into molten aluminium alloy in the mould by cooling plate cooling and towards the unidirectional curing in the top of this mould.As a result, obtain an ingot casting 206.The structure of this ingot casting 206 is subjected to the influence of cooling rate.Cooling rate is high more, then the size of Eutectic Silicon in Al-Si Cast Alloys crystal grain and primary silicon crystal crystal grain more little (these crystal grain can be generically and collectively referred to as " silicon crystal grain ").Cooling rate is low more, and then the size of these silicon crystal grains is big more.When using above-mentioned foundry equipment, near the highest cooling rate of part acquisition of this cooling plate, and the part at the top of close this mould obtains minimum cooling rate.Therefore, become less at the silicon crystal crystal grain that generates near the part place of cooling plate, and become bigger by the silicon crystal crystal grain that the part place near the top of this mould generates that is solidificated in of alloy by the curing of silumin.That is, can obtain one and have the wherein ingot casting of the graduate structure of size of silicon crystal grain.

Comprise the silicon that mass ratio is 6-25% as raw-material aluminum alloy.When the quality of silicon than content less than 6%, wearability suffers damage, and when the quality of silicon surpassed 25% than content, wearability no longer obtained the improvement suitable with the increasing amount of silicon.In addition, when the quality of silicon surpasses 25% than content, during forging, produce the crack, this means that forgeability suffers damage.In addition, shorten greatly the working life of cutting tool.

Preferably, this aluminum alloy is except comprising silicon, and also comprise Cu and the mass ratio that mass ratio is 0.3-7% is the Mg of 0.1-2% alone or in combination.These element age hardening aluminum alloys, thus the hardness and the mechanical property of the piston that is generated strengthened.More preferably, to comprise mass ratio be 1.5% or Ag still less or Sc to this aluminum alloy.

Because be used for the high temperature that the forging piston of explosive motor is subjected to the engine interior that causes owing to heat that the burning of fuel generates, require this piston at high temperature to have certain intensity.Therefore, this aluminum alloy preferably comprises the Ni that mass ratio is 0.1-2.0%, and known this element can improve intensity at high temperature.It also is effective adding Fe, Mn, Zr, Ti, W, Cr, V, Co, Mo etc. alone or in combination.

This aluminum alloy preferably comprises a kind of to reducing the size effective elements of Eutectic Silicon in Al-Si Cast Alloys crystal grain, for example Na, Ca, Sr or Sb.Can add these elements alone or in combination.It is favourable adding a kind of like this element, because can prevent the negative effect of large-sized Eutectic Silicon in Al-Si Cast Alloys crystal grain to the wearing and tearing of forgeability and machinery tools.

When generating primary silicon crystal crystal grain, usually P is attached in the aluminum alloy to reduce the size of this primary silicon crystal crystal grain.Yet when having Na or Ca in molten aluminium alloy, Na or Ca hinder the effect of P, cause reducing the size of this primary silicon crystal crystal grain.Therefore, Na or the Ca mass ratio in aluminum alloy on be limited to 50ppm.When the mass ratio of Na or Ca surpassed the quality of 50ppm, it is quite big that the size of primary silicon crystal crystal grain becomes.As a result, forgeability suffers damage, and has shortened the working life of milling cutter.

Can be by using described cooling plate to cool off by the ingot casting of using among above-mentioned molten alloy production the present invention, so that ingot casting has a structure, wherein the size of Eutectic Silicon in Al-Si Cast Alloys crystal grain and primary silicon crystal crystal grain is graduate and make crystal grain become big diminishing near the part of cooling plate in the part near the top of mould.

When the ingot casting that has by for example unidirectional curing Foundry Production one as the graduate structure of this crystallite dimension, cool off with the average-size (A) that obtains to be at least the Eutectic Silicon in Al-Si Cast Alloys crystal grain in 1.5 the top that is included in ingot casting and the ratio (A/B) that is included in this ingot casting, and average-size (A) is at least 4.0 μ m near the average-size (B) of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the part of a cooling plate.

In order to produce ingot casting with the graduate structure of above-mentioned crystallite dimension, can following control cooling rate.For example, as shown in Figure 3, during unidirectional curing casting, cool off obtaining to be at least 0.5 ℃/second cooling rate (E) when the point e of 5mm measures inwards, and obtain 0.85 or the littler 1mm and of making progress from measured cooling rate of this e (E) and bottom from the sidewall of this mould ratio E/F of the cooling rate (F) measured of the some f of 5mm inwards from curing mold from the downward 5mm in the top of curing mold and from the sidewall of this mould.

In the time of in cooling rate falls within above-mentioned scope, can produce forged material with above-mentioned structure.When this forged material is forged into one when being used for explosive motor and using piston, the forging piston of being produced has good forgeability, machinability and wearability.

This ingot casting is one usually and has the plate-like on upper and lower surface parallel to each other.Yet as long as this ingot casting has the graduate structure of above-mentioned crystal grain, this ingot casting can have Any shape according to the shape of the piston that will forge.For example, this ingot casting can have the uneven each other shape in its upper and lower surface, and perhaps, one or two in a kind of its upper and lower surface all has the shape of uneven protuberance and depressed part.The favourable part that this ingot casting has this uneven shape is, can reduce to be applied to the load on the forging die, and can form the piston with complicated shape by forging.

If desired, can before forging, carry out machining to this ingot casting.

If desired, can be after forging this ingot casting be carried out milling to obtain a surface with structure of requirement.When the outermost surface of this ingot casting comprises the silicon crystal grain of undesirable average-size, preferably to have one wherein the average-size of silicon crystal grain be that the ingot casting of graduate structure carries out milling and comprises the surface of the silicon crystal grain with desirable average-size up to obtaining one, thereby the ingot casting of using this formation is as a forged material.

Before forging this forged material being carried out one preheats.This preheat one fall within from 350 ℃ to from the solidus temperature of aluminum alloy (℃) temperature that deducts in the scope between the difference of 10 ℃ of gained carries out.This forged material is preheated bulk temperature up to this material to be reached the temperature in the above-mentioned scope and is after this forging.When being lower than when preheating under 350 ℃ the temperature one, enough plastic flow can not appear during the heat forged of forged material, and, may make forged material generation burning (burnt) (local melting) when being higher than when preheating under the temperature of above-mentioned difference one.When in forged material generation burning, the intensity of the product that is forged is weakened greatly, perhaps produces the defective that causes owing to local melting, for example hole and micro hole in this product.

Because usually forged material is carried out heat forged, this material is preheated, and a forging die also is heated.This heating-up temperature is 100 to 400 ℃.This heating-up temperature is determined according to the type of the shape that comprises forging product, forging equipment and the various forging parameters of type that constitute the alloy of material to be forged.Cross when low when this heating-up temperature, this forged material cools off with forging die, and the workability of this material is compromised, and causes the plastic flow deficiency of this material.On the contrary, when this heating-up temperature was too high, the intensity of this forging die reduced, and this mould tends to be ground away or break.Therefore, from the angle in working life of this forging die, too high heating-up temperature is not that institute is preferred.Preferably, after being applied to an oiling agent on this forging die, forge.

Forged material is carried out die forging.With reference to Fig. 5 an example of applied forging equipment in the present invention is described below.This forging equipment comprises that one forges bed 101, and is installed in upper mould 103, on the top die holder 102 and is installed in lower die 105 on the bottom die holder 106.Applied forging die comprises upper mould 103, lower die 105 and one stripper pin/knock pin 107 among the present invention.As shown in Figure 5, this forging die that use comprises upper mould 103 that is used to form a piston crown and the lower die 105 that is used to form a skirt section.Yet, can use one and comprise lower die that is used to form a piston crown and the forging die that is used to form the upper mould in a skirt section.If desired, a lubricant applying device can be set, this device comprise device 108, one sprayer whirligigs 109 that are used for flatly transporting a sprayer with one by one 110 oiling agent nozzle 104 that is connected with sprayer conveyor system 108.

In the present invention, forged material is placed forging die, the surface with the corresponding mould of piston crown is faced on the feasible surface that comprises the silicon crystal grain of big average-size.For example, when above-mentioned ingot casting is forged, this ingot casting is placed forging die, make this ingot casting upper surface facing to the surface of the corresponding mould of piston crown.When in a kind of opposite mode this ingot casting being placed this forging die, the front end in formed skirt section comprises the silicon crystal grain of big average-size, and formed oil ring groove partly comprises the silicon crystal grain of less average-size.Therefore in this case, can not obtain effect of the present invention.Promptly, the average-size that is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part (a) becomes less than 4 μ m, the average-size that is included in the primary silicon crystal crystal grain in the oil ring groove part becomes less than 15 μ m, the ratio (A/B) of the average-size (B) of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the average-size (A) that is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part and the fore-end that is included in the skirt section becomes less than 1.5, and the ratio (C/D) of the average-size (D) of the primary silicon crystal crystal grain in the average-size (C) that is included in the primary silicon crystal crystal grain in the oil ring groove part and the fore-end that is included in the skirt section becomes less than 1.3.As a result, the oil ring groove part does not have good machinability and wearability, and the fore-end in skirt section does not have good plastic fluidity during forging.

In manufacture method of the present invention, forged material is placed forging die, preferably, make the silicon crystal grain comprise big average-size the surface facing to the surface of the corresponding mould of piston crown, and the fore-end in skirt section preferably comprises the Eutectic Silicon in Al-Si Cast Alloys crystal grain with 3 μ m or littler average-size.The favourable part of this average-size is that this fore-end has good workability during heat forged.Promptly, comprise at the fore-end in skirt section under the situation of Eutectic Silicon in Al-Si Cast Alloys crystal grain with 3 μ m or littler average-size, even when during the thickness in this skirt section is forging, reducing, can not produce the crack at the fore-end that places forging die, and the die-filling characteristic of this fore-end can be not weakened yet yet.

Can carry out machining to the piston prefabricated component of formed forging.Yet, preferably this piston prefabricated component is heat-treated, for example artificial aging is handled, because can improve the mechanical property of the prefabricated component of being made by the alloy of a kind of Cu of comprising, Mg, Sc, Ag etc. by heat treatment.In artificial aging is handled, preferably, this piston prefabricated component stands solid solution (solid solution) to be handled, and wherein the piston prefabricated component is immediately following after 400-500 ℃ is heated 0.2-10 hour down, stand water quenching, and then at 150-250 ℃ of following tempering 0.2-20 hour.Handle the hardness that this prefabricated component can obtain to strengthen, mechanical property (for example, tensile strength and 0.2% yield strength) and fatigue strength by this artificial aging.

After this, the piston prefabricated component of this formation stands to comprise the processing that for example is used to form a piston pin hole, to the milling of a piston face be used to form the processing of the processing of oil ring groove, to produce final products (explosive motor is with forging piston) thus.

In manufacture method of the present invention, because forged material places forging die, make the silicon crystal grain comprise big average-size the surface facing to the surface of the corresponding mould of piston crown, the average-size (A) that is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part becomes and is at least 4 μ m, the average-size (C) that is included in the primary silicon crystal crystal grain in the oil ring groove part becomes and is at least 15 μ m, the ratio (A/B) of average-size (A) and the average-size (B) that is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the fore-end in skirt section becomes and is at least 1.5, and the ratio (C/D) of the average-size (D) of the primary silicon crystal crystal grain in the average-size (C) that is included in the primary silicon crystal crystal grain in the oil ring groove part and the fore-end that is included in the skirt section becomes and is at least 1.3.As a result, when oil ring groove is partly carried out milling, can prevent that the elongated shape chip is wrapped in the milling cutter and in the chuck of milling machine.Therefore can prevent from treating to produce cut on the piston face of milling.In addition, can prevent to pile up filamentous chip and prevent that whole chuck from being covered by chip in the bottom of milling machine.Therefore, can boost productivity.

The skirt section is not continuous along the whole periphery of this piston, but by wherein being inserted with a piston pin hole section of being divided into that is used for this piston is connected to the wrist pin on the connecting rod.Therefore, the milling in this skirt section is carried out in a kind of discontinuous mode, thereby has prevented the winding of chip in milling cutter.Therefore, be included in 0.67 times of average-size (A) of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part or littler as long as be included in the average-size (B) of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the fore-end in skirt section, and the ratio (C/D) of the average-size (D) of the primary silicon crystal crystal grain in the average-size (C) that is included in the primary silicon crystal crystal grain in the oil ring groove part and the fore-end that is included in the skirt section is at least 1.3, just can obtain gratifying chip manageability during milling.

Because can form the skirt section that thickness reduces by forging, do not need to be used to reduce the machining (milling) of skirt section thickness, perhaps can reduce the required machining allowance of machining.Therefore, can improve output based on the piston of (necessarily) material.In addition, because the machining needed time shortens, productivity improves.

Preferably, forged material stood a homogenization and handles before heat forged is forged the piston prefabricated component with the forgeability that improves this material and artificial aging is handled.In this homogenization is handled, at high temperature heat this forged material with the additional metal that in aluminum substrate, distributes equably, for example Cu or Mg.This metal is added in the forged material with the mechanical strength that strengthens piston to be formed and increases the intensity of this piston in the motor that is used under the high temperature, and carries out microsegregation (microsegregate) during casting.Handle by this homogenization, can guarantee the forgeability of forged material, and can obtain to be subjected to the homogenization of the mechanical property of the forging piston prefabricated component that artificial aging handles.This homogenization handle can one fall within from 400 ℃ to from the solidus temperature of an alloy to be used (℃) temperature that deducts in the scope between the difference of 10 ℃ of gained carried out 1 to 30 hours.

According to the shape of the type of an alloy to be used or piston to be formed, the preheating of the forged material that carries out before forging can be played and be handled the effect similar effects that is obtained by the homogenization to forged material.For example, when forged material being carried out one hour or during the preheating of longer time, can obtain and handle the effect similar effects obtained by homogenization.Simultaneously, according to the shape of the type of an alloy to be used or piston to be formed, that carries out after forging can play and handle the effect similar effects that is obtained by the homogenization to forged material forging the heat treatment of piston prefabricated component.For example, when this forging piston prefabricated component stands long solution treatment during artificial aging is handled, can obtain and the effect similar effects that is obtained by the homogenization processing.

Describe effect of the present invention in detail below with reference to the example of using the forged material of forged material that a forged material that forms by unidirectional curing casting, forms by continuous casting and by the formation of metal (forever) mold casting.

Example 1 and 2:

The alloy 1 with solidus temperature of one 549 ℃ shown in the table 1 stands unidirectional curing casting by equipment shown in Figure 2, thereby to form ingot casting (external diameter: 77mm, the thickness: 30mm) (example 1) as a forged material.The alloy 1 with solidus temperature of one 528 ℃ shown in the his-and-hers watches 1 carries out unidirectional curing casting by equipment shown in Figure 2, thereby to form ingot casting (external diameter: 110mm, the thickness: 30mm) (example 2) as a forged material.Casting condition is shown in the table 2.In each example in example 1 and 2, K-type thermocouple is set in the position of mould shown in Figure 3 to measure the cooling rate of this ingot casting during curing.

Each above-mentioned forged material stands 8 hours homogenization under 490 ℃ handles, and uses the forging equipment shown in Fig. 5 to forge into a piston prefabricated component by heat forged then.With this forged material place this forging equipment forging die so that the upper surface of forged material (ingot casting) be ingot casting do not forged into piston crown in the face of the surface of the cooling plate of forging equipment, and make that the bottom surface of ingot casting is that the skirt section is forged on the surface in the face of the cooling plate of forging equipment of ingot casting.Forging condition is shown in the table 3.

In example 1, the external diameter of the forging piston prefabricated component of production is 78mm, and the thickness in the skirt section of this prefabricated component is 3.5mm, and the forging load during forging is 430t.In example 2, the external diameter of the forging piston prefabricated component of production is 111mm, and the thickness in the skirt section of this prefabricated component is 4mm, and the forging load during forging is 670t.

By the crack of visual observation edge and the generation of plastic flow equidirectional, because the formability in the skirt section of each piston prefabricated component is estimated in the generation of underfill that insufficient plastic flow of the front end in skirt section causes during forging and hairline.

Formed piston prefabricated component carries out artificial aging under the condition shown in the table 4 handles.

Utilize Rockwell hardness tester to measure the hardness of this formed piston prefabricated component.Measurement is included in the average-size of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part, measures the average-size of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the fore-end that is included in the skirt section, and calculates the ratio of last average-size and back one average-size.And, measure the average-size that is included in the primary silicon crystal crystal grain in the oil ring groove part, measure the average-size of the primary silicon crystal crystal grain in the fore-end that is included in the skirt section, and calculate the ratio of last average-size and back one average-size.For the ease of relatively, utilize an image analyzer to measure the maximum chord length of each silicon crystal grain (MAXLNG).

In the present invention, observe the sample of a preparation at a microscopically, and utilize an image analysis processor that image analysis is carried out on the surface of observing with a structure observational technique.The mean value of equivalent diameter (circle-equivalent diameter) (average cross-section by the crystal grain that will find in the surface of observing is decreased to the area of a circle and the HEYWOOD diameter that obtains as crystal grain diameter with this diameter of a circle) is considered as average grain size.

Maximum chord length is meant the extreme length of the silicon crystal grain that uses a vernier caliper measurement.When two silicon crystal crystal grain have identical HEYWOOD diameter, and one of them crystal grain is when having a bigger MAXLNG, and this silicon crystal crystal grain with big MAXLNG in the form of sheets or needle-like.

The oil ring groove part of formed piston prefabricated component is carried out the milling test under condition shown in the table 5, and aspect shape and the manageability chip is being estimated.Under the conditions shown in Table 6 the surface roughness of the inwall of this oil ring groove is estimated then.Use a Compax milling cutter shown in Figure 4 (artificial diamond's milling cutter made of stones) and carry out the milling test.Utilize the surface roughness meter, measure the surface roughness of the oil ring groove of this piston prefabricated component along the direction parallel (that is, along the direction surperficial parallel) with piston head with the milling direction.

Then, near acquisition one sample of this oil ring groove, and under condition shown in the table 7, at ambient temperature this sample is carried out a pin-mill then and decrease test, to measure the wear extent of a pin.

Table 8 illustrates the result of the cooling rate of above-mentioned measurement.Table 9 illustrates the Eutectic Silicon in Al-Si Cast Alloys crystal grain that is included in the ingot casting and the average-size of primary silicon crystal crystal grain.Table 12 illustrates the hardness (HRB) of this piston prefabricated component, the formability in skirt section, the chip shape that oil ring groove partly produces, the manageability of chip, the surface roughness of the inwall of oil ring groove and near the wear extent of the sample of the acquisition of oil ring groove part.

Comparative examples 1 and 2:

Be the continuous casting rod (comparative examples 1) of 82mm and be the continuous casting rod (comparative examples 2) of 115mm from the diameter of making by an alloy 1 shown in the table 1 from the diameter of making by an alloy 2 shown in the table 1.Continuous casting utilizes disclosed Pneumatic type thermal direct casting fabrication technique in JP-B SHO 54-42847 under the conditions shown in Table 10 and carries out.In comparative examples 1, formed ingot casting is carried out 8 hours homogenization at 495 ℃ handle, carry out cutting then so that diameter is decreased to 77mm.In comparative examples 2, formed ingot casting is similarly handled so that diameter is decreased to 110mm.After this, each ingot casting is cut into the workpiece with 30mm thickness, and formed workpiece is used as forged material.In this comparative examples 1 and 2, this forged material is forged respectively with the condition identical with condition in example 1 and 2.Yet during forging, each forged material is placed in the forging die in the mode different with the mode described in example 1 or 2.In comparative examples 1 and 2, formed forging piston prefabricated component is carried out the artificial aging processing respectively and carries out machining then with the condition identical with condition in example 1 and 2.

Table 11 illustrates the measurement result of the average-size of the average-size of Eutectic Silicon in Al-Si Cast Alloys crystal grain and primary silicon crystal crystal grain.Table 12 illustrates the result of the evaluation of carrying out in the mode similar to the mode of example 1 or 2.

Table 1 (mass percent %)

	Si	Cu	Mg	Ni	Fe	Mn	Ti	Sr	Ca	P
											Alloy 1	9.6	3.0	0.46	-	0.18	-	-	0.005	-	-
Alloy 2	19.2	1.1	1.10	0.9	0.44	0.40	0.13	-	0.002	0.010

Table 2

Project	Example 1	Example 2
			1. the molten alloy temperature that in the molten alloy container, records	740 ℃	800 ℃
2. the material of mould and molten alloy container	Lumiboard	Lumiboard
			3. the height difference between the liquid level of mould top and the molten alloy in the molten alloy container	150mm	150mm
4. the temperature of cooling plate before cast	100 ℃	200 ℃
			5. cooling water inflow	6L/min	7L/min
6. molten alloy inlet diameter	12mm	10mm
			7. the air temperature in the electric furnace	770 ℃	820 ℃
8. the top, top of mould and the air temperature of sidewall	680 ℃	700 ℃
			9. casting process: 1) cast 2) cooling beginning condition 3) cooling termination condition 4) cooling plate operation 5) material takes out	After 15 seconds, close obstruction piece; In the time of 500 ℃, begin water-cooled; In the time of 100 ℃, finish water-cooled; In the time of 150 ℃, reduce cooling plate; Naturally fall.	After 17 seconds, close obstruction piece; In the time of 500 ℃, begin water-cooled; In the time of 100 ℃, finish water-cooled; In the time of 250 ℃, reduce cooling plate; Naturally fall.

Table 3

Project	Example 1	Example 2
			1. forge bed	The 630t-mechanical press	The 800t-mechanical press
2. forging die temperature
			1) drift temperature	150℃	170℃
2) die temperature	250℃	300℃
			3. lubricant oil type	Graphite lubricating oil (GLO)	With a left side
4. the pre-heating temperature of forged material	400℃	450℃

Table 4

Project	Example 1	Example 2
			1. solution treatment condition 1) heating-up temperature	495℃	505℃
2) keep temperature	2 hours	2 hours
			2. tempered condition 1) heating-up temperature	200℃	180℃
2) keep temperature	6 hours	10 hours

Table 5

	Example 1	Example 2
			1. milling cutter type 2. rotating speeds 3. amount of feeding 4. cutting depth 5. milling oil type 6. chips are estimated the position	Compax cutter cutter head section (Nose) the water-soluble milling oil of radius R 2mm 600rpm 0.5mm/rev 0.2mm is around the oil ring groove place	Left together with a left side with left 400rpm with a left left side together

Table 6

	Example 1	Example 2
			1. milling cutter type 2. rotating speeds 3. depth of cut 4. milling oil type	The water-soluble milling oil of 600rpm 0.06mm/rev as shown in Figure 4	Left together with left 400rpm with a left side

Table 7

Project	Content
		1) testing apparatus	Abrasion meter TRI-S500 type (Takachiho Seiki)
2) test method	Pin-dish method
		3) disk material	The ADC12 molding material
4) lubricant oil	Mission oil
		5) load that applies	5kgf
6) slip speed	0.25m/sec
		7) sliding time	60 minutes
8) Xiao shape	φ7.9mm-h20mm

Table 8

	The measuring position	Measured value	Example 1	Example 2
					Cooling rate ℃/second	e	E	2.6	4.1
f	F	6.2	5.5
				Ratio		E/F	0.42	0.75

Table 9

Table 10

	Comparative examples 1	Comparative examples 2
			1. ingot casting diameter	82mm	115mm
2. the head length header overhang length that suspends	10mm	With a left side
			3. molten alloy temperature	720℃	820℃
4. casting speed	200mm/min	180mm/min
			5. cooling water inflow	15L/min	25L/min
6. lubricant oil type	Castor oil	With a left side
			7. lubricant oil flow velocity	0.4cc/min	0.1cc/min
8. gas type	Air	Air
			9. gas flow rate	0.5L/min	0.1L/min

Table 11

Table 12

	Example 1	Example 2	Comparative examples 1	Comparative examples 2
					1. piston cross-section hardness (HRB)	75	69	74	68
2. skirt section formability	○	○	○	○
					3. the chip shape of annular groove part	The part shape	The part shape	Elongated shape	Elongated shape
4. the chip manageability of annular groove part	○	○	×	×
					5. the surface roughness of the inwall of annular groove (Ra: μ m)	0.9	1.1	3.5	5.4
6. the wear extent of annular groove part sample (μ m)	19	3	34	7
					Overall assessment	○	○	×	×

The evaluation criterion of the formability in skirt section

Project	Not	Be
			1. crack, skirt section	○	×
2. the underfill of skirt section fore-end	○	×
			3. the minute crack of skirt section fore-end	○	×

The evaluation of chip shape

Be clearly shown that as table 8,, in forged material, do not have primary silicon crystal crystal grain having used by being that 2.6 ℃/second and ratio (E/F) are in the example 1 of the forged material that casting forms under 0.42 the condition in the measured cooling rate of an e; The average-size (HEYWOOD diameter) that is included in oil ring groove part and is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the fore-end in skirt section is respectively 4.7 μ m and 2.3 μ m; Ratio (A/B) is about 2.Be clearly shown that as table 11 in the comparative examples of having used by alloy 1 formed minor diameter continuous casting rod 1, the average-size that is included in oil ring groove part and is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the fore-end in skirt section is respectively 2.0 μ m and 2.0 μ m; Ratio (A/B) is 1, show this piston prefabricated component not wherein the silicon crystal grain size along the graduate structure of thickness direction.Be included in the average-size of the average-size of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part of piston prefabricated component of comparative examples 1 less than the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part of the piston prefabricated component that is included in example 1.Be clearly shown that as table 12 in example 1 and comparative examples 1, the formability in skirt section is all fine.In example 1, the chip that partly produces from oil ring groove has a part shape.On the contrary, in comparative examples 1, the chip that partly produces from oil ring groove has an elongated shape, and the manageability of hence one can see that chip is very poor.In comparative examples 1, the inwall of oil ring groove has bigger surface roughness, and oil ring groove partly has relatively poor wearability.Usually, when the inwall of oil ring groove had bigger surface roughness, this oil ring groove was by piston ring scuffing, and this oil ring groove becomes big.As a result, this piston cooperates obliquely with oil ring groove, and this causes the problems such as wearing and tearing on cylinder inner wall.When the gap between piston and the cylinder became big owing to the relatively poor wearability of oil ring groove part, it is big that consumption of lubricating oil becomes, and piston and cylinder can not cooperate in mode hermetically each other, thereby reduced motor output.Therefore, when the piston prefabricated component of comparative examples 1 was made a piston, formed piston was considered to not have gratifying characteristic.

Contrast table between example 2 and the comparative examples 2 is understood following content.In example 2, the cooling rate that records at an e is 4.1 ℃/second, and ratio (E/F) is 0.75.In example 2, the average-size (A) that is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part is 6.9 μ m; The average-size (B) that is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the fore-end in skirt section is 2.8 μ m; Ratio (A/B) is 2.5; The average-size (C) that is included in the primary silicon crystal crystal grain in the oil ring groove part is 23.9 μ m; The average-size (D) that is included in the primary silicon crystal crystal grain in the fore-end in skirt section is 15.7 μ m; Ratio (C/D) (pact) is 1.5.Be clearly shown that as table 11 in comparative examples 2, the average-size (A) that is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part is 2.6 μ m; The average-size (B) that is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the fore-end in skirt section is 2.5 μ m; Ratio (A/B) (pact) is 1.0; The average-size (C) that is included in the primary silicon crystal crystal grain in the oil ring groove part is 17.7 μ m; The average-size (D) that is included in the primary silicon crystal crystal grain in the fore-end in skirt section is 18.3 μ m; Ratio (C/D) (pact) is 1.0, show this piston prefabricated component not wherein the silicon crystal grain size along the graduate structure of thickness direction.As mentioned above, be included in the average-size of Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part of piston prefabricated component of comparative examples 2 and primary silicon crystal crystal grain less than the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part of the piston prefabricated component that is included in example 2 and the average-size of primary silicon crystal crystal grain.In example 2 and comparative examples 2, the formability in skirt section is all fine.In example 2, the chip that partly produces from oil ring groove has a part shape.On the contrary, in comparative examples 2, the chip that partly produces from oil ring groove has an elongated shape, and the manageability of chip is relatively poor thus, and the inwall of oil ring groove has bigger surface roughness.In comparative examples 2, because it is less to be included in the average-size of Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part and primary silicon crystal crystal grain, the chip that partly produces from oil ring groove has an elongated shape, the manageability of chip is relatively poor, the inwall of oil ring groove has bigger surface roughness, and the wear extent of the sample that is partly obtained by oil ring groove is bigger.

Comparative examples 3:

The piston prefabricated component passes through the production of metal (forever) mold casting by alloy shown in the table 11 and alloy 2.Comparative examples 3 has been used two types mold, promptly category-A (corresponding to the thickness of the part in skirt section: 3.5mm) and category-B (corresponding to the thickness of the part in skirt section: 6mm).These two kinds of moulds are identical with applied forging die in the example 1 in shape.The internal diameter of this category-A and category-B mould is identical with shape.

The piston prefabricated component passes through Foundry Production by this category-A and category-B mould under the casting condition shown in the table 13.Skirt section zero defect (soundness) to formed piston prefabricated component is estimated.The result is shown in the table 14.Table 15 shows the average-size measurement result of Eutectic Silicon in Al-Si Cast Alloys crystal grain and primary silicon crystal crystal grain.

Table 13

	Alloy 1	Alloy 2
			1. casting temperature	720℃	810℃
2. die temperature	400℃	420℃
			3. mould coating reagent	Releasing agent (die coat)	With a left side
4. riser height	200mm	With a left side

Table 14

Skirt section thickness	Alloy 1	Alloy 2
			3.5mm	×	×
6.0mm	○	○

Illustrate:

Zero: do not have underfill in the skirt section

*: owing to the misrun in skirt section has defective

Table 15

	The measuring position	Measured value	The HEYWOOD diameter		MAXLNG
							Alloy 1	Alloy 2	Alloy 1	Alloy 2
			The average-size μ m of Eutectic Silicon in Al-Si Cast Alloys crystal grain	The oil ring groove part	A	3.6					5.1	6.4	8.8
The fore-end in skirt section	B	3.6					5.2	6.5	8.8
				Ratio		A/B				1.0	1.0	1.0	1.0

The result of table 14 shows, comprise that when forming one by the arbitrary alloy in alloy 1 and 2 its thickness is 3.5mm by metal (forever) mold casting, during the piston prefabricated component in promptly identical skirt section with the thickness in the skirt section of the piston prefabricated component that forges, because misrun and in the front end generation underfill in skirt section, and formed prefabricated component does not have the suitable quality of quality with the piston prefabricated component that forges.This result shows that also when the thickness in skirt section was 6mm, this skirt section had zero defect.As mentioned above, the piston prefabricated component that forms by metal (forever) mold casting does not have feature like the feature class with the piston prefabricated component that forges.Because be included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part of piston prefabricated component that the average-size of Eutectic Silicon in Al-Si Cast Alloys crystal grain in the oil ring groove part of piston prefabricated component of comparative examples 3 and primary silicon crystal crystal grain is included in example 1 or 2 no better than and the average-size of primary silicon crystal crystal grain, can think that the oil ring groove of piston prefabricated component of comparative examples 3 partly has good milling.Yet, under the situation of comparative examples 3, because the thickness in skirt section can not reduce, and needs relatively large Milling Process surplus, so can not obtain high productivity.

Comparative examples 4:

Alloy shown in the table 12 is melted in a melting solid unit, and formed molten alloy is poured into a cylindrical swage (external diameter: 300mm, total length: 350mm, internal diameter: 115mm, the degree of depth: 250mm), thereby have the columned ingot casting (length of the zero defect part that does not comprise hole of this ingot casting: 150mm) of 115mm external diameter to form one.During casting, the temperature of molten alloy remains on 800 ℃, and mould is heated to 300 ℃ in advance.Formed cylindric ingot casting is carried out homogenization under 490 ℃ handled 8 hours.Then, the periphery of ingot casting is carried out cutting removing defective part, thereby form a pole with 110mm external diameter.This pole is cut into the workpiece with 30mm thickness, and the workpiece that will form is as forged material.

With two types be the C class (corresponding to the thickness of the part in skirt section: 4.0mm) and the D class (corresponding to the thickness of the part in skirt section: forging die 6mm) is produced the piston prefabricated component by heat forged, and the piston that is obtained has identical external diameter thus.Before heat forged, earlier this forged material is preheated to 450 ℃.Formability to the skirt section of formed piston prefabricated component is estimated.Under the condition identical, carry out heat forged with condition in the example 2 shown in the table 3.The result is shown in the table 16.Obtain a sample from the front end in the skirt section of each prefabricated component, and observe the structure of this sample, to measure the average-size of Eutectic Silicon in Al-Si Cast Alloys crystal grain and primary silicon crystal crystal grain thus.The result is shown in the table 17.

Table 16

Skirt section thickness	4mm	6mm
			Skirt section zero defect evaluation	×	○
Annotate	Crack at the place, skirt section

Table 17

The fore-end in skirt section
		The average-size of Eutectic Silicon in Al-Si Cast Alloys crystal grain	8.7μm
The average-size of primary silicon crystal crystal grain	33.4μm

Average-size: HEYWOOD diameter

The result shows, when the average-size of Eutectic Silicon in Al-Si Cast Alloys crystal grain or primary silicon crystal crystal grain was big, forgeability reduced, and can not produce a finished product that good wearability and the easily broken fragility of chip are arranged.The result also shows; when the average-size of Eutectic Silicon in Al-Si Cast Alloys crystal grain or primary silicon crystal crystal grain is big; as under the situation of metal (forever) mold casting, must during forging, form the skirt section of big thickness, and must carry out machining to reduce the thickness in this skirt section thus to this skirt section then.

Industrial applicibility

As mentioned above, according to the present invention, can produce a kind of forging piston that is used for explosive motor that comprises oil ring groove part and a skirt section, the average-size that wherein is included in Eutectic Silicon in Al-Si Cast Alloys crystal grain in the fore-end in skirt section and primary silicon crystal crystal grain is littler, and it is bigger to be included in the average-size of these crystal grain in the oil ring groove part. This skirt section has the same good malleability in skirt section with the piston that is become by a kind of continuous casting clavate of minor diameter, and therefore can reduce the thickness in this skirt section. In addition, the oil ring groove part has the same good chip manageability of oil ring groove part with the piston that forms by casting during milling, and this oil ring groove has littler surface roughness and has good mar proof.

Can not be by using traditional minor diameter continuous casting rod to carry out warm and hot forging or producing the piston of aforesaid forging by metal (forever) mold casting. Yet the present invention can provide a kind of forging piston that is used for explosive motor with the advantage that is obtained by warm and hot forging and metal (forever) mold casting.

Make forging piston of the present invention by a kind of manufacture method in conjunction with warm and hot forging and artificial aging processing by a kind of material that obtains by unidirectional curing casting.

Applied aluminium alloy is except comprising original additional elements (namely among the present invention, Si, Cu and Mg) outside, can also comprise for the element that further improves artificial age-hardening's performance, such as Ag or Sc, with a kind of be used to improving stable on heating element, such as Fe, Ni, Ti, Cr, V, Zr, Mn, Co, Nb or Mo. These elements can be added individually or in combination. By adding so a kind of element, to compare with other parts, the characteristic of oil ring groove part, skirt section, head surface and piston pin part can better be improved.

Therefore, can provide a kind of cheap high-performance to forge piston, and can provide quality uniform high-performance enginer.

Claims (8)

1. one kind is the forging piston that is used for explosive motor that the aluminum alloy of the silicon of 6-25% is made by comprising mass ratio, this piston comprises an oil ring groove part and a skirt section, the ratio (A/B) of the average-size (B) of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the average-size (A) that wherein is included in the Eutectic Silicon in Al-Si Cast Alloys crystal grain in this oil ring groove part and the fore-end that is included in this skirt section is at least 1.5, and this average-size (A) is at least 4 μ m.

2. forging piston according to claim 1, it is characterized in that, the ratio (C/D) of the average-size (D) of the primary silicon crystal crystal grain in the average-size (C) that is included in the primary silicon crystal crystal grain in the oil ring groove part and the fore-end that is included in the skirt section is at least 1.3, and this average-size (C) is at least 15 μ m.

3. forging piston according to claim 1 and 2 is characterized in that, it is the Mg of 0.1-2% that described aluminum alloy comprises Cu and the mass ratio that mass ratio is 0.3-7%.

4. forging piston according to claim 1 and 2 is characterized in that, described aluminum alloy comprises the Ni that mass ratio is 0.1-2.5%.

5. a manufacturing is used for the method for the forging piston of explosive motor, comprises the steps:

To comprising mass ratio is that the molten aluminium alloy of the silicon of 6-25% carries out unidirectional curing casting to produce an ingot casting as the forged material with each other relative first surface and second surface thus, and the average-size that wherein is included in the silicon crystal grain in the first surface is different from the average-size that is included in the silicon crystal grain in the second surface;

This forged material is preheated;

This forged material is placed a forging die, and the surface corresponding to piston crown of this mould is faced on the feasible surface that comprises the silicon crystal grain of big average-size, thus this forged material is forged into a piston prefabricated component;

This piston prefabricated component is carried out artificial aging to be handled; With

The piston prefabricated component that forms is carried out machining, to make a forging piston that is used for explosive motor thus.

6. method according to claim 5, it is characterized in that, unidirectional curing casting be included as the average-size (A) that obtains to be at least the Eutectic Silicon in Al-Si Cast Alloys crystal grain in 1.5 the top that is included in ingot casting be included in this ingot casting near the ratio (A/B) of the average-size (B) of the Eutectic Silicon in Al-Si Cast Alloys crystal grain in the part of a cooling plate and be at least the average-size (A) of 4.0 μ m and the cooling carried out.

7. method according to claim 5, it is characterized in that, unidirectional curing casting comprises: for obtain be 0.85 or littler, from the downward 5mm in top that solidifies mould and from the sidewall of curing mold inwards the cooling rate (E) measured of the some e of 5mm with make progress 1mm and from the cooling carried out of the ratio (E/F) of the cooling rate (F) of the some f measurement of 5mm inwards of the sidewall of curing mold, wherein cooling rate (E) is at least 0.5 ℃/second in bottom from curing mold.

8. according to each described method in the claim 5 to 7, it is characterized in that the temperature in a scope that falls between the difference that deducts 10 ℃ of gained from 350 ℃ to the solidus temperature from aluminum alloy is carried out described preheating.

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