JP2014037622A - Continuously cast rod and forging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a continuously cast rod of an Al-Sn based alloy with a fine structure free from the formation of primary crystal Si.SOLUTION: Disclosed is a continuously cast rod comprising, by weight, 12 to 20% Si, 0.5 to 6% Cu, 0.1 to 6% Mg, Fe and Mn so as to satisfy Fe>Mn and Fe+Mn=0.3 to 2%, Ti and Zr so as to satisfy Ti/Zr=0.06 to 1 and also Ti+Zr≤0.3% and 0.005 to 0.025% Sr, and the balance Al with impurities, and produced by a heat insulation mold.

Description

  The present invention relates to an Al—Si alloy continuous cast bar and a forged product using the same.

  Hypereutectic Al-Si alloys containing 12.6% or more of Si are interspersed with primary Si crystal grains in the base material of the aluminum alloy, resulting in high wear resistance and sliding properties.・ Because it shows high temperature strength, it has been used for pistons and compressors. However, according to the conventional DC casting method, when the Si content is increased, the primary crystal Si is increased, and there is a problem that workability is lowered.

  In Patent Document 1, in the hot top DC casting method, P and Ca are added as primary Si refinement agents, and Mg, Sr and Ba are added as primary crystal refinement aids. It is disclosed that an ingot of a hypereutectic Al-Si alloy in which the crystal Si can be refined and the primary crystal Si is uniformly distributed is obtained. However, even the thing of patent document 1 has made primary crystal Si of 10-20 micrometers, and even if it is primary crystal Si of such a magnitude | size, there exists a possibility of having a bad influence on forge processability.

JP 2010-12470 A

  In view of the above situation, the present invention is characterized by providing a continuously cast rod of an Al—Si alloy having a fine structure free from primary Si and a forged product using the same.

  In order to achieve the above-mentioned object, the continuous casting rod according to the first aspect of the present invention is characterized in that Si is 12 to 20 wt%, Cu is 0.5 to 6 wt%, Mg is 0.1 to 6 wt%, and Fe and Mn are Fe. > Mn and Fe + Mn = 0.3-2 wt%, Ti and Zr contain Ti / Zr = 0.6-1, Ti + Zr ≦ 0.3 wt%, Sr 0.005-0.025 wt%, the balance being Al and It is an impurity and is characterized by being manufactured with a heat insulating mold.

  The continuous cast bar according to the second aspect of the present invention is 12 to 20 wt% Si, 0.5 to 4 wt% Cu, 0.1 to 6 wt% Mg, Fe> Mn Fe> Mn and Fe + Mn = 0.3 ~ 2wt%, Ti and Zr contain Ti / Zr = 0.06 ~ 1, Ti + Zr≤0.3wt%, Ca contains 0.005 ~ 0.02wt%, the balance is Al and impurities, manufactured by heat insulation mold It is characterized by that.

  The continuous cast bar according to the invention of claim 3 is made of Si of 12 to 20 wt%, Cu of 0.5 to 6 wt%, Mg of 0.1 to 6 wt%, Fe and Mn of Fe> Mn and Fe + Mn = 0.3. ~ 2 wt%, Ti and Zr contain Ti / Zr = 0.06 to 1 and Ti + Zr ≤ 0.3 wt%, Sr and Ca contain Sr + Ca = 0.004 to 0.03 wt%, the balance being Al and impurities, It is characterized by being manufactured with a heat insulating mold.

  A forged product according to a fourth aspect of the invention is characterized in that the continuous cast bar according to any one of the first to third aspects is hot or cold forged.

  The continuous cast bar according to the first aspect of the present invention has the effect of refining and stabilizing the structure by containing 0.005 to 0.025 wt% of Sr, and the cooling rate can be increased by manufacturing with a heat insulating mold. Even if Si is contained in an amount of 12 to 20 wt%, a fine structure free from primary Si can be obtained.

  The continuous cast bar according to the invention of claim 2 has the effect of refining and stabilizing the structure by containing 0.005 to 0.02 wt% of Ca, and the cooling rate can be increased by manufacturing with a heat insulating mold. Even if Si is contained in an amount of 12 to 20 wt%, a fine structure free from primary Si can be obtained. Since Ca is less expensive than Sr, the cost can be reduced.

  The continuous cast bar according to the invention of claim 3 has an effect of refining and stabilizing the structure by containing Sr and Ca of Sr + Ca = 0.004 to 0.03 wt%, and a cooling rate by being manufactured with a heat insulating mold. This makes it possible to form a fine structure in which primary Si does not appear even if Si is contained in an amount of 12 to 20 wt%. By adding Sr and Ca in combination, a fine structure can be stably obtained and the total amount can be reduced as compared with the case of adding Sr and Ca alone.

  Since the forged product according to claim 4 is hot or cold forged from the continuous cast bar according to any one of claims 1 to 3, forging workability is good because it is a fine structure with no primary crystal Si, Precise forged products can be obtained stably. Since Si is contained in an amount of 12 to 20 wt%, the wear resistance and high temperature strength are high.

It is a photograph of the section of Examples 1-4 and comparative examples 1 and 2 of the continuous casting stick concerning the present invention. It is the table | surface which put together the result of the casting method of an Example and a comparative example, an ingot diameter, an alloy component, T6 room temperature strength, and a forge test. It is a schematic diagram which shows an example of the continuous casting apparatus used for manufacture of the continuous casting rod of this invention. It is a schematic diagram which shows the other example of the continuous casting apparatus used for manufacture of the continuous casting rod of this invention. It is a figure which shows an example (piston) of the forged goods using the continuous casting rod of this invention, Comprising: (a) is a front view, (b) is a side view, (c) is a bottom view. It is a photograph which shows the result of upsetting and forging the continuous cast bar of Example 1. It is a table | surface which shows an Example in case an ingot diameter is large, and a comparative example. It is a photograph of the section of an example and a comparative example shown in the table of FIG. It is the table | surface which put together the result of having experimented how an ingot structure changes when the quantity of Sr is changed. It is a photograph of the section of an example and a comparative example shown in the table of FIG. It is a table | surface which shows the Example which changed the ingot diameter and the quantity of Sr. It is a photograph of the section of the example shown in the table of FIG. It is a graph which shows the relationship between the quantity of Sr, and tensile strength. It is the table | surface which put together the result of having experimented how the ingot structure changes when the quantity of Ca is changed. It is a photograph of the cross section of the Example and comparative example which are shown in the table | surface of FIG. It is the table | surface which put together the result of having experimented how the ingot structure changes when the quantity of Ca and Sr is changed. It is a photograph of the cross section of the Example shown in the table | surface of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The continuous cast bar of the present invention is a so-called hypereutectic Al-Si alloy containing 12 to 20 wt% of Si, using either Sr and Ca, or both Sr and Ca, and using a heat insulating mold As a result of casting, a fine structure with no primary crystal Si is produced. Further, the continuous cast bar of the present invention is added with a predetermined amount of Fe, Cu, Ti, Mn, Mg, Zr in order to obtain properties such as strength, heat resistance, wear resistance, and workability. Hereinafter, the action and content of each element will be described.

Si: 12-20 wt%
Si is an element that contributes to the improvement of low thermal expansion and wear resistance. However, if added in a large amount, coarse primary crystal Si is crystallized, and the strength, toughness and workability of the material are lowered.
Accordingly, in the present invention, in order to obtain a sufficient effect, the lower limit is set to 12 wt%, and in order to ensure sufficient toughness and workability, the upper limit is set to 20 wt%.

Cu: 0.5 to 6 wt%, or 0.5 to 4 wt% (when adding only Ca)
Cu is an element that contributes to improving high-temperature strength by precipitation of Al ₂ Cu. However, when added in a large amount, coarse compounds and porosity are generated, which reduces the strength and toughness and increases the specific gravity.
Therefore, to obtain the minimum required strength at 200 ° C., the lower limit is 0.5 wt%, and in order to prevent the generation of coarse compounds and porosity and to suppress the increase in specific gravity, the upper limit is 6 wt%. . When only Ca is added without adding Sr, if the amount of Cu is more than 4 wt%, the effect of refining and stabilizing the structure due to the addition of Ca will not be exhibited, so the upper limit of Cu is set to 4 wt%.

Mg: 0.1-6 wt%
Mg is an element that contributes to improving the strength by precipitation of Mg ₂ Si, but if added in a large amount, the compound becomes coarse and the strength and toughness are lowered. Therefore, Mg is 0.1 to 6 wt% as a range in which the effect of improving the strength is recognized and no coarse compound is generated.

Fe, Mn: Fe> Mn and Fe + Mn = 0.3-2 wt%
Fe is an element that contributes to high temperature strength improvement by precipitation of a compound with Al. A simple substance crystallizes as an Al-Fe-Si compound. Mn is also an element for improving the high temperature strength, and when added simultaneously with Fe, an Al ₆ (Fe, Mn) compound is formed. Since the Al—Fe—Si compound works for high-temperature strength, Fe is made more than Mn. Further, if Fe is added in an amount of 2 wt% or more, the compound becomes coarse and the strength and toughness are reduced. If 0.3 wt% or less, the effect of improving the high temperature strength cannot be sufficiently obtained. Yes.

Ti, Zr: Ti / Zr = 0.6-1 and Ti + Zr ≦ 0.3 wt%
Ti and Zr are both elements that contribute to refinement of the structure and heat resistance. In particular, Zr contributes to improving the strength after forging, so the amount of Zr added is larger than that of Ti. When the total amount of Ti and Zr is 0.3 wt% or more, coarse crystals are generated, so Ti + Zr ≦ 0.3 wt%.

Sr: 0.005-0.025 wt%
Sr has a function of refining the structure of the additive element such as Si and stabilizing the structure. When the Sr content is less than 0.005 wt%, this effect becomes unstable, and when it is more than 0.025 wt%, porosity may be generated. Therefore, Sr is set to 0.005 to 0.025 wt%.

Ca: 0.005-0.02 wt%
Ca, like Sr, has a function of refining the structure of additive elements such as Si and stabilizing the structure. If the Ca content is less than 0.005 wt%, this effect becomes unstable, and if it is more than 0.02 wt%, porosity may be generated. Therefore, Ca was 0.005 to 0.025 wt%.

Sr, Ca: Sr + Ca = 0.004 to 0.03 wt%
Ca is less expensive than Sr, but the effect may be unstable. By adding Sr and Ca in combination, the unstable part of Ca is supplemented with a small amount of Sr having the same effect, and the structure is refined.・ Stable effects can be obtained. Moreover, the total addition amount can be reduced rather than adding Sr and Ca each independently. If the combined amount of Sr and Ca is less than 0.004 wt%, the effect is unstable, and if it exceeds 0.03 wt%, porosity may occur, so Sr + Ca = 0.004 to 0.03 wt% It was.

About Zn Aluminum alloys for die casting such as ADC12Z have a large amount of flow and are relatively inexpensive, but contain Zn as an impurity. If Zn is contained, problems such as a decrease in corrosion resistance occur. It wasn't. Even if the continuous cast bar of the present invention contains Zn, such a problem does not occur, and it becomes a fine and stable structure as in the case of containing no Zn. For this reason, an aluminum alloy for die casting can be used as a raw material, thereby reducing costs. The content of Zn is not limited, but is preferably about 0.8 wt% or less.

  The contents of Cu and Fe are preferably changed according to the use environment of a product manufactured from the continuous casting rod of the present invention. Specifically, when strength at 200 ° C. or lower is required, Cu is added to nearly 5%, and when strength at 200 ° C. or higher is required, Fe is preferably added to near 1%.

An example of a continuous casting apparatus used for casting the continuous casting rod of the present invention is shown in FIG. This continuous casting apparatus has a hot water receiving part 1 for pouring molten metal and a heat insulating mold 2 penetrating vertically in a lower part of the hot water receiving part 1. A graphite mold was used as the material of the heat insulating mold 2. A heat insulating layer 3 is provided on the upper side wall of the heat insulating mold 2, and a water cooling jacket 4 is provided around the lower side wall. The water cooling jacket 4 has a water supply port 4b, a cooling water chamber 4c, and a cooling water injection nozzle 4a. The cooling water injection nozzle 4 a is configured to inject cooling water toward the lower end 2 a outside the heat insulating mold 2, and locally cools the lower end 2 a of the heat insulating mold 2. Further, from the viewpoint of improving the local cooling effect of the lower end portion 2a of the heat insulating mold 2, the thickness on the lower side of the heat insulating mold 2 is made thinner than that on the upper side. Molten metal M enters from the upper part of the heat insulating mold 2 and is cooled by the inner side 2b of the lower end part of the heat insulating mold 2 to form a solidification interface Mc. Continuous casting while receiving at 6.
As described above, by locally cooling the lower end portion 2a outside the heat insulating mold 2, the width d of the solid-liquid coexisting temperature region becomes smaller than that of the conventional heat insulating continuous casting method.
The cooling water 5 sprayed to the lower end portion 2a of the heat insulating mold 2 flows down while forming the flowing water portion 5a along the surface of the ingot Ms.

  As described above, the lower end portion 2a of the heat insulating mold 2 is locally cooled with the cooling water 5, and the ingot Ms is cooled to 45 to 65 ° C by the cooling water (running water portion 5a) flowing down along the surface of the ingot Ms. It is possible to cool at a high cooling rate of / s. As a result, the solidification of the molten aluminum alloy is completed quickly, the ingot surface becomes smooth, and the solid-liquid coexistence temperature range becomes narrow inside the ingot, so that the growth of intermetallic compounds is suppressed and the internal structure is fine. It becomes uniform. The cooling rate is obtained from a change in temperature measured by the thermocouple 7 by inserting the thermocouple 7 into the center of the ingot Ms from above, lowering the thermocouple 7 in synchronization with the cradle 6. The cooling rate can be changed by appropriately adjusting the casting rate and the amount of cooling water.

  FIG. 4 shows another embodiment of the continuous casting apparatus. Explaining the difference from FIG. 3, the water cooling jacket 4 has a mold cooling water injection nozzle 14 a and an ingot surface cooling water injection nozzle 14 b in two stages, and is injected from the mold cooling water injection nozzle 14 a. The lower end 2a of the mold is locally cooled with the cooled water, and the cooling water 5 is sprayed from the ingot surface cooling water spray nozzle 14b toward the surface of the ingot Ms. The cooling water sprayed from the ingot surface cooling water spray nozzle 14b cools the surface of the ingot Ms so as to break the falling water film formed by the flow 5a of the cooling water sprayed to the lower end 2a of the heat insulating mold 2, thereby secondary The cooling effect is enhanced and the temperature gradient in the vicinity of the solidification interface can be increased, and the cooling ability of the mold inner lower end S can be further enhanced.

  The mold shape is not limited to the straight type having the same mold inner peripheral diameter in the vertical direction as shown in FIGS. 3 and 4, but the lower side may be a tapered type having a large diameter, and the cross-sectional shape is only circular. Alternatively, an irregular cross section may be used.

The above-described continuous casting apparatus was used to cast continuous casting rods of the alloy components shown in the table of FIG. 2, and the internal structure was observed, the T6 room temperature strength was measured, and the forging test was performed.
Example 1 is obtained by adding Ca, Example 2 is obtained by adding Sr, Example 3 is obtained by adding Sr and Ca in combination, and Example 4 is obtained by adding Sr and Zn. It is. Comparative Example 1 was cast with a heat-insulating mold in the same manner as in Examples 1 to 4, and neither Sr nor Ca was added, and Comparative Example 2 was cast by a DC casting method and Sr was added. The T6 room temperature strength is the maximum strength when a tensile test is performed in a state where the strength is increased by performing a heat treatment called T6 treatment.

As is clear from the photograph in FIG. 1, the structures of Examples 1 to 4 to which either or both of Sr and Ca are added are fine structures in which primary Si does not appear. Example 4 containing Zn also has a fine structure in which primary Si does not appear as in Examples 1 to 3. About Example 1, when the size of the crystallization thing (black dots in a figure) was measured, the average value was 2 micrometers. Other embodiments are also miniaturized to the same extent as in the first embodiment. In Examples 1 to 4, no porosity was generated. Examples 1 and 2 and Examples 3 and 4 have different ingot diameters (Examples 1 and 2 are 105 mm, Examples 3 and 4 are 60 mm). A fine structure free from primary Si can be obtained stably.
On the other hand, in the structure of Comparative Example 1, the crystallization product is needle-like and larger as compared with Example 1, and the generation of porosity is also observed. About Comparative Example 1, when the size of the crystallized product was measured, the average value was 8 μm. Thus, even if it casts with a heat insulation mold, when neither Sr nor Ca is added, it is difficult to stably obtain a fine structure.
In the structure of Comparative Example 2, primary crystal Si of about 20 μm is dispersed and crystallized, and a needle-like crystallized product is also observed, which is completely different from Examples 1-4. Even if Sr is added in this way, when cast by the DC casting method, the primary crystal Si of about 20 μm is crystallized because the cooling rate is not fast.

The piston 7 having the shape shown in FIG. 5 was manufactured by forging the continuous casting rods of Examples 1 to 4. As a result, it was confirmed that defects such as cracks did not occur and the forgeability was good. Further, when upset forging was performed on Example 1, as shown in FIG. 6, no cracking occurred even when crushed to 72%.
On the other hand, when upsetting forging was performed for Comparative Example 2, cracking occurred in a little 60%. The reason why the forgeability is inferior is considered to be due to the coarse structure.

  When T6 room temperature intensity | strength is seen, Example 2-4 shows the high value of the substantially same grade, and it turns out that intensity | strength is higher than the comparative examples 1 and 2. FIG. In particular, Example 4 containing Zn showed the highest value. From this, it can be seen that high strength can be obtained without primary crystal Si.

FIGS. 7 and 8 show the results of experiments on what difference is seen in the ingot structure when Sr is added and when Sr is not added when the ingot diameter is as large as 176 mm.
As apparent from the photograph of FIG. 8, Example 5 to which Sr was added had smaller Si particles than Comparative Example 3 to which Sr was not added. In Comparative Example 3 in which Sr is not added, large Si particles as indicated by arrows in the figure are confirmed, but in Example 5 to which Sr is added, such large Si particles are not seen.

  9 and 10 show the results of an experiment to see what difference is seen in the ingot structure when the amount of Sr is changed. As is apparent from the photograph of FIG. 10, primary Si was confirmed in Comparative Example 4 in which Sr was not added and Comparative Example 5 in which 0.004 wt% Sr was added, and Comparative Example 6 in which 0.05 wt% Sr was added. Then, porosity occurred. In Example 6 in which 0.02 wt% of Sr was added, a fine structure without primary Si and porosity was obtained. From the above results, it can be seen that the amount of Sr added is small at 0.004 wt%, and porosity is generated when the amount of Sr is too large. Although the experiment was conducted with two types of ingot diameters of 60 mm and 120 mm, the tendency was the same even if the ingot diameter was different.

  Furthermore, as shown in FIGS. 11, 12, and 13, the amount of Sr was changed within a range of 0.005 to 0.025 wt%, and the ingot structure was observed and the tensile strength was measured. As is clear from the photograph of FIG. 12, Examples 7 to 12 to which Sr was added in the range of 0.005 to 0.025 wt% all had a fine structure with neither primary Si nor porosity. Moreover, as shown in the graph of FIG. 13, when Sr was added in the range of 0.005-0.025 wt%, it was confirmed that it had a substantially constant high tensile strength of 400 MPa or more. Although the experiment was conducted with two types of ingot diameters of 60 mm and 120 mm, the tendency was the same even if the ingot diameter was different.

  14 and 15 show the results of an experiment to see what difference is seen in the ingot structure when the amount of Ca is changed. As apparent from the photograph of FIG. 15, primary crystal Si was confirmed in Comparative Example 7 in which 0.004 wt% of Ca was added, and porosity was generated in Comparative Example 8 in which 0.025 wt% of Ca was added. In Example 13 to which 0.009 wt% of Ca was added, a fine structure having neither primary Si nor porosity was obtained. From the above results, it can be seen that the amount of Ca added is small at 0.004 wt%, and porosity is generated when the amount of Ca is too large.

  FIGS. 16 and 17 show the results of an experiment on what difference is seen in the ingot structure when the amounts of Sr and Ca are changed when Sr and Ca are added in combination. As is clear from the photograph in FIG. 17, it was confirmed that a fine structure having neither primary Si nor porosity was obtained within the range of Sr + Ca = 0.004 to 0.03 wt%.

  As described above, the continuous casting rod of the present invention has the effect of refining and stabilizing the structure by adding Sr and Ca, and the solidification of the molten aluminum alloy is completed quickly by casting with a heat insulating mold. In combination with this, a fine structure free from primary Si can be obtained. Thereby, workability such as forging is remarkably improved. The present invention can obtain the same effect even if the ingot diameter is different, and is also effective for a large diameter ingot diameter of 150 mm or more. In addition, the forged product obtained by forging the continuous cast bar of the present invention contains a large amount of additives such as Si and Cu, so that it has excellent strength and wear resistance and has a fine structure free from primary Si. It has good properties and can be suitably used as a piston, a compressor, or the like.

  The present invention is not limited to the embodiments described above. The alloy components can be appropriately changed within the scope described in the claims. Moreover, you may contain the component which is not described in a claim. The diameter of the continuous casting rod is not particularly limited. The specific shape and application of the forged product are arbitrary, and the forging method is not particularly limited.

2 Insulation mold 7 Piston (forged product)
Ms ingot (continuous casting rod)

Claims (4)

  12-20 wt% Si, 0.5-6 wt% Cu, 0.1-6 wt% Mg, Fe> Mn Fe> Mn and Fe + Mn = 0.3-2 wt%, Ti and Zr Ti / Zr = A continuous cast bar characterized by comprising 0.06 to 1 and Ti + Zr ≦ 0.3 wt%, containing 0.005 to 0.025 wt% of Sr, the balance being Al and impurities, and manufactured by a heat insulating mold.   12-20 wt% Si, 0.5-4 wt% Cu, 0.1-6 wt% Mg, Fe> Mn Fe> Mn and Fe + Mn = 0.3-2 wt%, Ti and Zr Ti / Zr = A continuous cast bar characterized by comprising 0.06 to 1 and Ti + Zr ≦ 0.3 wt%, Ca containing 0.005 to 0.02 wt%, the balance being Al and impurities, and being manufactured by a heat insulating mold.   12-20 wt% Si, 0.5-6 wt% Cu, 0.1-6 wt% Mg, Fe> Mn Fe> Mn and Fe + Mn = 0.3-2 wt%, Ti and Zr Ti / Zr = Continuous casting, characterized in that 0.06 to 1 and Ti + Zr ≦ 0.3 wt%, Sr and Ca are contained in Sr + Ca = 0.004 to 0.03 wt%, the balance being Al and impurities, and manufactured by a heat insulating mold rod.   A forged product obtained by hot or cold forging the continuous cast bar according to any one of claims 1 to 3.