GB2096514A - Deposition of metal on aluminium-based alloys - Google Patents

Abstract

A layer of metal other than aluminium is deposited onto an aluminium alloy with the use of a surfacing material based on an alloying element. Deposition is effected at a heat source heat output of 10<3> to 10<5> W/cm<2>, and the surfacing material is added to the welding pool in an amount of from 20 to 98% by weight. Subsequently the deposited metal is remelted at least once, with the volume of the welding pool being increased by a factor of 1.2-10 each time the deposit is remelted.

Description

SPECIFICATION Deposition of metal on aluminium-based alloys The present invention relates to the art of welding and is particularly concerned with a method of forming a deposit on a n alu m an aluminium-based alloy. The invention is particularly useful in the manufacture of internal combustion engines for transport vehicles, aircraft and marine engines, and stationary engines, as well as in the aircraft industry and rocket building.

Aiuminium-based alloys are used in all the above-mentioned industries. The ever increasing power of such engines requires that the alloys used in their manufacture have a correspondingly higher resistance.

One of the additional requirements that have to be met by engine parts and assemblies which are designed to take up high loads and at the same time are subjected to impact loads at elevated temperatures, is wear resistace. However, to further improve the wear resistance of parts made from aluminium alloys to meet given operating conditions, it becomes necessary to increase the content of the alloying elements to an extent that will not allow such parts to be manufactured by applying conventional methods such as casting, forging, and stamping. In this respect the deposition of a layer of a metal having a higher wear resistance seems to be the most suitable method of strengthening such parts.However, the scope of practising of the welding techniques with respect to welding aluminium alloys are also limited since adding great amounts of alloying elements to the metal being deposited is not possible to accomplish by applying processes known in the art.

The present invention provides a method of depositing a metal other than aluminium on aluminium-base alloy with the use of a surfacing material based on alloying element, wherein the deposition of metal is carried out with a heat output of the heat source of from 103 to 105 W per sq cm and the welding material being added to the welding pool in an amount of from 20 to 98 wght percent, whereafter the deposited metal is remelted, with the welding pool volume being increased 1.2 - 10.0 times, each time when the deposited metal is remelted.

This permits the use of a surfacing material based on alloying elements including those whose melting point is higher than that of the aluminium. Such elements are iron, nickel, cobalt, manganese, and chromium.

While adding the material to the welding pool it is expedient to divide the process into several steps. At the beginning the amount of alloying element should constitute 20 - 98% of the welding pool weight. A uniform distribution of the surfacing material through the whole volume of the welding pool can be achieved by using a more concentrated heating source in comparison with that which is normally used to form a welding pool of the same volume.

In particular, in the case of electric arc welding the welding current is increased 1.5 - 3 times with the welding speed being simultaneously increased 3 - 10 times. (Any disturbances in the formation of the weld seam, such as undercuttings, which may occur during the process are burnished later in the course of the operation.) If the amount of alloying elements in the surfacing material constitutes 20% it will be sufficient to increase the welding current 1.5 times and the welding speed 3 times, whereas with the amount of the alloying elements constituting 98% the current and the speed of deposition should preferably be increased 3 and 10 times respectively. It is to be noted, however, that the parameters of metal deposition are increased only at that step of the process at which the surfacing material is added to the welding pool.The subsequent remelting that follows is continued without addition of the surfacing material and therefore at this step normal parameters are used. As used herein the term "normal parameters" means such parameters as for example: a metal layer 5 mm thick is deposited with a current of 250 - 300 A and the speed of deposition of 16 - 20 m/h.

While remelting the metal deposited at the first step of the process the volume of the welding pool is increased 1.2 - 10.0 times which is necessary for providing a uniform distribution of alloying elements.

This method of deposition improves wear-resistance, heat-resistance, and other operating characteristics of the machine parts subjected to local loads at elevated temperatures, which makes it possible to improve technical-and-economic indicies of, for example, internal combustion engines at the expense of a greater extent to which the engine power can be augmented, to increase their service life 1.5 to 2.0 times, to save such elements as nickel and cobalt which are in short supply and which are commonly used to improve operating characteristics of aluminium-based alloys.

Example 1 A wear-resistant layer was deposited in the zone of the first compression ring of an internal combustion engine piston, with the ring diameter being 110 mm. The piston was made by casting an aluminium-based alloy comprising, by weight, 12.1% silicon, 2.2% copper, 0.8% magnesium, 1.3% nickel, 0.4% iron, 0.2% manganese, and 0.1% titanium, the remainder being aluminium.

The deposition was effected by argon-arc welding with the use of an iron-based surfacing material which was applied in the form of 1.2 mm solid wire comprising, by weight: 0.1% carbon, 1.9% manganese, and 0.8 silicon, the balance being iron.

The weld penetration for a piston of the above type was to be 4 - 5 mm.

The weld material was added under the following operating conditions: Welding arc heat output 0.7 x 104W/cm2 (welding current = a.c. 500 A, 50 Hz, are stream voltage = 15 - 1 8V) Tungsten electrode diameter 8 mm Shielding gas consumption 101/mien Speed of deposition 180 m/h Speed of wire feeding 190 m/h The above operating conditions made it possible to add to the deposit (welding pool) 50 wt% of alloying elements, with the base material of the deposit being an intermetallic iron/aluminium compound having elevated brittleness. It should also be noted that the said intermatallic compound is formed by dissolving the aluminium-based alloy in the molten iron-based surfacing material at a temperature of about 1500 C.

The intermetallic compound thus formed was then diluted in aluminium alloy, which was effected by remelting the deposit, with the welding pool volume being increased by a factor of 7, and the speed of deposition being decreased from 180 m/h to 54 m/h. Thereafter, the deposit was remelted again with the welding pool volume increased by a factor of 4, and the speed of deposition decreased from 54 m/h to 36 mlh.

The thus-formed deposit has the following ingredients (by weight) 11.6%silicon,5.3% iron, 2.1% copper, 0.76% magnesium,1.21% nickel, 0.21% manganese, and 0.08% titanium, the balance being aluminium.

The deposit was tested for impact toughness, tensile strength, and Brinall hardness. The test results are given below.

Tensil strength, MPa 180 Brinell hardness, HB: at a temperature of 20 C 125 at a temperature of 2500C 80 Notch toughness, MJ/m2 0.1 The deposit was subjected to a metallographic investigation which showed that the deposit had an intermetallic-compound-reinforced heterophase composite structure, which ensured a high elastic modulus of the deposit, this modulus being close to the elastic modulus of cast iron. The deposit in the zone of the first compression ring was tested directly on the engine. The test results showed that the wear resistance of such pistons was 4 times higher than that of pistons which were not strengthened in the same way. Comparison tests of pistons strengthened with the deposit and of pistons provided with an insert of "niresist" iron were also conducted.The tests showed that the wear resistance of the pistons having the deposit was 10 to 20% higher than that of the pistons provided with inserts of "niresist" cast iron.

Example 2 A wear resistant layer was deposited on the joint plane of an automobile engine block head made by casting an aluminium-based alloy comprising (by weight): 8.7% silicon, 0.2% manganese, 0.03% nickel, 0.03% titanium, 0.3% magnesium,0.6% iron, and 0.1% copper, the remainder being aluminium.

The deposition was effected by means of a laser beam applying argon-shielded welding process with the use of surfacing material in the form of a manganese-based alloying powder containing, by weight, 10.8% iron, 15.6% chromium, and 20.3% silicon, the balance being manganese.

The said welding material was added under the following operating conditions: Laser beam heat output 103W/cm2 Laser beam operating diameter 2 mm Consumption of argon 4 - 61/mien Speed of deposition 80 m/h The above operating conditions made it possible to add to the metal being melted 20 weight percent of the manganese-based alloying material, with the alloying elements being being contained in the deposited metal in the form of large intermetallic bodies.

To provide for a uniform destribution of the alloying elements in the deposit it was remelted, with the welding pool volume being increased by a factor of 10, which was accomplished by decreasing the speed of deposition from 80 m/h to 10 m/h.

The thus-formed deposit was composed, by weight, of 8.6% silicon. 3.3% manganese, 0.03% nickel, 0.02% titanium, 0.2% magnesium,0.6% iron, 0.1 copper, and 0.8% chromum, the balance being aluminium.

The deposit was tested for notch toughness, tensile strength, and Brinell hardness. The results of the test are given below.

Tensile strength MPa 200 Brinell hardness, HB 120 Notch toughness, MJ/m2 0.1 T he deposit was subjected to a metallographic investigation which showed that the deposit had a composite heterophase structure reinforced by a manganese and chromium-based intermetallic compound.

Comparison tests of an automobile engine block head strengthened with the wear-resistant deposit in the zone of the exhaust outlets and of a cylinder block head without such a wear-resistant deposit conducted.

The tests which were conducted on an operating engine showed that the heat-resistance of the strengthened cylinder block head was a factor of 2 higher than that of the head without such strengthening, which allows the service life of an engine to be increased by factor of 2.

Example 3 A wear-resistant layer was deposited in the first compression ring zone of an internal combustion engine piston having a diameter of 100 mm. The piston was manufactured by casting an aluminium alloy containing, by weight, 12.1% silicon, 1,6% copper, 0.8% magnesium,1.4% nickel, 0.5% iron, 0.1% of manganese, and 0.03% of titanium, the remainder being aluminium.

The deposition was effected by electron beam spray coating with the use of a nickel-based surfacing material, in a vacuum of about 10-4 mm Hg, applying a plasma welding technique, whereafter a wear-resistant layer was melted. To this end the coated surface of the piston was exposed to an electron beam having a heat output of 1 W/cm2 and a diameter of 10 mm, with the speed of deposition being 220 m/h. These operating conditions allowed 98 wt.% of nickel to be included in the deposit.

To provide for a uniform distribution of alloying elements the deposit was remelted, with the volume of the welding pool being increased by a factor of 6, which was accomplished by decreasing the speed of deposition from 220 m/h to 80 m/h. The resulting deposit was remelted again, with the volume of the welding pool being increased by a factor of 7, the speed of deposition being further decreased from 80 m/h to 25 m/h.

The thus-formed deposit contained, by weight: 11.9% silicon,7.0% nickel, 1.1% copper, 0.8% magnesium, 0.4% iron, 0.1% manganese, and 0.03% titanium, the balance being aluminium.

The deposit was tested for notch toughness, tensile strength, and Brinell hardness. The test results are given below.

Tensile strength, MPa 210 Brinell hardness, HB 130 Notch toughness, MJ/m2 0.1 A comparison test of the piston strengthened with the deposit in the zone of the first compression ring and the piston having an insert of "niresist" cast iron in the same zone, directly on the engine, showed that the wear-resistance of pistons strengthened with the deposit increased by a factor of 1.2.

Example 4 A wear-resistant layer was deposited on a 110 mm piston of an internal combustion engine in the zone of the inner chamber edge. The piston was made by casting an aluminium alloy comprising, by weight, 12.1% silicon, 2.2% copper, 0.8% magnesium,1.3% nickel, 0.4% iron, 0.2% manganese, and 0.1% titanium, the balance being aluminium.

The deposition was carried out by applying a plasma welding process with the use of argon as a plasma-forming gas and a surfacing material in the form of powdered alloying material comprising, by weight,20.0% iron, 4.0% cobalt,10.0% chromium, 5.0% manganese, 20.0% silicon, and 2.0% vanadium, the balance being aluminium.

The alloying material was added to the deposit under the following operating conditions: Plasma heat source heat output 104W/cm2 Welding current 260 A, 50 Hz Arc stream voltage 15-18 V Consumption of shielding gas 5 mm Speed of deposition 150 m/h The above operating conditions allowed 20% by weight of alloying elements to be added to the deposit, with the alloying elements being present in the deposit in the form of separate brittle composite intermetallic bodies.

To uniformly distribute the alloying elements in the deposit it was remelted, with the welding pool volume being increased by a factor of 1.2, which was accomplished by decreasing the speed or deposition from 20 to 16 m/h.

The resulting deposit was composed, by weight, of 11.9% silicon, 7.0% nickel, 1.6% copper, 0.8% magnesium,0.4% iron,0.1 manganese, and 0.03% of titanium, the balance being aluminium.

The deposit was tested for notch toughness, tensile strength, and Brinell hardness. The test results are given below.

Tensile strength, MPa 210 Brinell hardness, HB 130 Notch toughness, MJ/m2 0.1 The deposit was subjected to metallographic investigation which showed that it had a fine-grained composite structure with a dendritic intermetallic matrix.

For the purpose of comparison, two pistons were tested directly on an engine in operation, one piston being strengthened with the deposit, and the other not being so strengthened. The test showed that the thermocyclic strength of the edges of the pistons strengthened with the deposit was 50% higher than that of the pistons which were not strengthened.

Example 5 A wear-resistant layer was deposited on a 130 mm piston of an internal combustion engine in the zone of the first compression ring. The piston was made of cast aluminium alloy comprising (by weight): 20.0% silicon, 0.3% manganese, 1.5% nickel, 0.2% titanium, 0.5% magnesium,1.3% iron, and 3.0% copper, balance aluminium.

The deposition was effected by applying an argon-arc welding process with the use of an iron-based surfacing material which was used in the form of an iron-based surfacing material which was used in the form of 1.6 mm powder-core wire having an iron sheath.

The iron sheath was composed, by weight, of 0.1% carbon, 1.9% manganese, and 0.8% silicon, the remainder being iron. The core flux contained (by weight): 25% chromium, 12.0% molybdenum, 13.0% vanadium, 20.0% titanium, and 13.0% cobalt, the balance being silicon.

The surfacing material was added under the following operating conditions: Welding arc heat output 0.8 x 10 W/cm2 Welding current 600 A, 50 Hz Arc stream voltage 18 -20 V Diameter of tungsten electrode 10 mm Consumption of shielding gas 101/mien Speed of deposition 180 m/h Speed of wire feeding 180 m/h The amount of alloying elements which was possible to add under the above operating conditions amounted to 30 wt%, the base of the deposit being in intermetallic composition of the alloying elements and aluminium.

To dissolve the resulting intermetallic compound in the matrix metal the deposit was remelted, with the welding pool volume being increased by a factor of 7.5, which was accomplished by decreasing the speed of deposition from 180 to 45 m/h. The thus-formed deposit was remelted again with the welding pool volume being increased by a factor of 5, the speed of deposition being decreased from 45 to 28 m/h.

The thus-formed deposit comprised, by weight, 19.0% silicon, 0.3% manganese, 1.4% nickel, 0.21% titanium, 0.5% magnesium,5.0% iron, 2.8% copper, 0.2% chromium, 0.1% molybdenum, 0.1% vanadium, and 0.1% cobalt, the balance being aluminium.

The deposit was tested for notch toughness, tensile strength, and Brinell hardness. The test results are given below: Tensile strength, MPa 220 Brinell hardness, HB 135 Notch toughness, MJ/m2 0.1 A comparison test of the piston reinforced with the deposit and a piston which was not so reinforced showed that the wear resistance of the first was 1.5 times higher than that of the second.

Example 6 A wear-resistant layer was deposited on the piston of an internal combustion engine in the zone of the first compression ring, the diameter of the piston being 120 mm. The piston was made from aluminium alloy containing, by weight, 0.1% silicon, 0.04% manganese, 0.9% nickel, 0.04% titanium, 1.4% magnesium,0.9% iron, and 2.0% copper, balance aluminium.

The deposition was effected by applying a plasma welding technique with the use of argon as a plasma-forming and shielding gas. As a surfacing material use was made of a composite 2 mm wire consisting of an iron (50 wt.%) and nickel (50 wt.%) - based core and an aluminium sheath.

The surfacing material was introduced under the following operating conditions: Plasma heat source heat output 0.7 x 104 W/cm2 Welding current 500 A, 50 Hz Arc stream voltage 16-17V Diameter of tungsten electrode 8 mm Consumption of shielding gas 91/mien Speed of deposition 200 m/h Speed of wire feeding 280 m/h The above operating conditions allowed 60 wt.% of alloying elements to be added, with the base of the deposited metal being an intermetallic phase of iron/nickel/aluminium having an elevated brittleness.

The resulting intermetallic compound was dissolved in the aluminium-based alloy to produce an intermetallic composition having an elevated stability and strength. This was achieved by remelting the deposit, with the welding pool volume being increased by a factor of 9, the speed of deposition being reduced from 200 to 30 m/h.

The thus-formed deposit contained, by weight, 0.1% silicon, 0.03% manganese, 3.4% nickel, 0.04% titanium, 1.4% magnesium,3.5% iron, and 2.0% of copper, the balance being aluminium.

The deposit was then tested for notch toughness, tensile strength, and Brinell hardness. The test results are given below: Tensile strength, MPa 250 Brinell hardness, BH 140 Notch toughness, MJ/m2 1.2 A comparison test of the piston strengthened with the deposit and of a piston which was not strengthened showed that the wear resistance of the former was 5 times higher than that of the latter.

Example 7 (negative) The method was carried out in general as described in Example 2. However, the amount of an alloying element added to the deposit consituted 15 weight percent. In this case the alloying elements were present in the deposit both in the form of separate intermetallic inclusions and unmelted particles. Therefore, it was no use continuing the process, since otherwise non-uniform distribution of the alloying elements would have occurred, which would result in an elevated brittleness of the deposited layer.

Example 8 (negative) The method was carried out in general-as described in Example 3. This time, however, the spray-coated surface of the piston was remelted with the aid of an electron beam having heat output of 106 W/cm2.

Increase in the heat output of the heat source to a level higher than the recommended upper limit caused more intensive evaporation of the molten metal, which led to loss of the alloying elements in the deposited layer and affected the process of formation thereof, as well as leading to the formation of deposit on the peepholes of the vacuum chamber.

Example 9 (negative) The method was carried out in a similar way to Example 1. However, the heat output of the welding arc was 0.8 x 103 W/cm2, i.e. lower than the recommended lower limit, which was not sufficient to melt down the melting material and therefore did not allow the process to be continued.

Example 10 (negative) The method was carried out in general as described in Example 1, except that deposition was effected with the welding pool volume being increased by a factor of 12. This resulted in the alloying elements formed in the deposited layer large separate brittle intermetallic inclusions which caused a sharp decrease in the notch toughness of the deposit. The further remelting of the welding pool did eliminate this defect, as the temperature of the welding pool in this case could not be raised higher than 900 C, while the said intermediate inclusions had a melting point in the range from 1300 to 1400 C.

Claims (2)

1. A method of forming a weld deposit on an aluminium-based alloy with the use of a surfacing material comprising at least one alloying element, wherein the deposition is conducted with heat source heat output of from 103 to 105 W/cm2 and the surfacing material is added to the welding pool in an amount of from 20 to 98 weight percent, whereafter the weld deposit is remelted at least once, with the volume of the welding pool being increased by a factor of 1.2 to 10 each time the deposit is remelted.

2. A method of forming a weld deposit on an aluminium-based alloy, substantially as described in any of Examples 1 to 6.