1. A heat treatment process for casting aluminum-silicon alloy is applicable to Al-Si-Mg series alloy, and is implemented between the cutting process step and the machining step of casting aluminum alloy, and is characterized in that: the heat treatment process adopts the process of homogenizing 460 plus or minus 5 ℃/6 to 8H plus 545 plus or minus 5 ℃/10 to 12H, cooling the mixture to 260 ℃ along with the furnace, then cooling the mixture in air, and finally carrying out T6 (quenching 538 plus or minus 5 ℃/6 to 8H aging 155 plus or minus 5 ℃/4 to 6H).

Background

At present, the specific process flow for casting aluminum alloy at home and abroad generally comprises the following steps: smelting, casting, cutting, heat treatment, machining and other process steps, for the heat treatment process, the main common processes are T6, T5, T4, T7, T8 and the like. For the automotive industry, gravity cast products are mainly made by T6 or T5 to improve alloy strength and plasticity. The alloys for which gravity casting is primarily suitable are of the Al-Si-Mg series.

For some products with low strength and plasticity caused by insufficient melting and deterioration and grain refinement after conventional heat treatment, for example, for AlSi7Mg0.3(b) alloy, the testing requirements of a single-cast test bar are that Rm is more than or equal to 270MPa, Rp0.2 is more than or equal to 190MPa, A is more than or equal to 7 percent, the performance of sampling a casting body requires that Rm and Rp0.2 are not less than 80 percent of the single-cast test bar, A is not less than 50 percent of the single-cast test bar, and Sr content is 0.006 percent, deterioration is insufficient, and after conventional heat treatment (538 ℃/7H, 155 ℃/4H aging), the testing results of the body sample are as follows: rm is 250MPa, Rp0.2 is 230MPa, A is 0.8 percent, the plasticity is unqualified, so the product requirement cannot be met by adopting the conventional heat treatment, the defects of the previous working procedures are made up, the defective products are saved, and a new heat treatment process is required to be found.

For some products requiring high strength and plasticity, such as single-cast test bars Rm of AlSi7Mg0.3(a) alloy are more than or equal to 280MPa, Rp0.2 is more than or equal to 190MPa, A is more than or equal to 10 percent, the performance requirement of sampling a casting body is that Rm and Rp0.2 are not less than 80 percent of the single-cast test bars, and A is not less than 50 percent of the single-cast test bars, but the performance requirement can not be met by adopting the conventional T6 treatment, generally the single-cast test bars Rm of the AlSi7Mg0.3(a) alloy are 300MPa, Rp0.2 is 190MPa, and A is 8 percent, so a heat treatment method capable of improving the strength and the plasticity of the alloy must be found.

Disclosure of Invention

The invention aims to provide a heat treatment process for casting aluminum-silicon alloy, which overcomes the technical problems in the prior art and solves the problems of insufficient strength and plasticity of a casting which is required to be high and large-scale scrapping of products caused by insufficient strength and plasticity of the products due to poor alloy deterioration and refining effects. The process of the invention can not only meet the requirements of strength and plasticity of the alloy, but also excavate the maximum potential of the alloy, and has a promoting effect on the research of high-strength cast aluminum alloy.

In order to achieve the above object, the present invention is realized by:

a heat treatment process for casting aluminum-silicon alloy is applicable to Al-Si-Mg series alloy, and is implemented between the cutting process step and the machining step of casting aluminum alloy, and is characterized in that: the heat treatment process adopts the process of homogenizing 460 plus or minus 5 ℃/6 to 8H plus 545 plus or minus 5 ℃/10 to 12H, cooling the mixture to 260 ℃ along with the furnace, then cooling the mixture in air, and finally carrying out T6 (quenching 538 plus or minus 5 ℃/6 to 8H aging 155 plus or minus 5 ℃/4 to 6H).

The process has the advantages that:

the process of the invention introduces homogenization treatment into the cast aluminum alloy, adopts double homogenization treatment, so that the distribution of compounds and phases is more uniform, and then carries out T6 treatment, so that the strength and the plasticity of the alloy are greatly improved. The problems that the strength and the plasticity of the casting are insufficient, and the strength and the plasticity of the product are insufficient due to poor alloy deterioration and refining effects, so that a large amount of products are scrapped are solved. The process of the invention can not only meet the requirements of strength and plasticity of the alloy, but also excavate the maximum potential of the alloy, and has a promoting effect on the research of high-strength cast aluminum alloy.

Drawings

FIG. 1 is a metallographic structure (200X) of a material deficient in metamorphism by conventional heat treatment.

FIG. 2 is a metallographic structure (200X) of an insufficiently degenerated material according to the invention.

FIG. 3 is a metallographic structure (200X) of an AlSi7Mg0.3(a) alloy of high strength and plasticity.

Detailed Description

The invention discloses a heat treatment process for cast aluminum alloy, which is arranged between a cutting process step and a machining step of a specific process flow of the cast aluminum alloy (the specific process flow of the cast aluminum alloy generally comprises the process steps of smelting, casting, cutting, heat treatment, machining and the like).

The invention focuses on the idea of introducing homogenization treatment into the cast aluminum alloy to improve the strength and plasticity of the alloy and expounded the advantages of double homogenization, so that the potential of the cast aluminum alloy is brought into full play. The invention comprises the following steps: homogenizing at 460 + -5 deg.C/6-8H +545 + -5 deg.C/10-12H, cooling to 260 deg.C, air cooling, and performing T6 (quenching at 538 + -5 deg.C/6-8H for 155 + -5 deg.C/4-6H).

The effect of the process of the invention is further illustrated by two examples.

1. The AlSi7Mg0.3(b) alloy is in metallurgical structure due to insufficient metamorphism, insufficient structure refinement and the like in the smelting process. The AlSi7Mg0.3 alloy has overheating phenomenon at 565 ℃, so the homogenization temperature is not too high, but not too low, and the homogenization effect is not enough, so the alloy adopts 545 +/-5 ℃; from the phase diagram of the aluminum-silicon alloy, it can be seen that the alloy is rapidly dissolved in the matrix at around 460 ℃, which results in non-uniform and insufficient dissolution of many compounds and phases into the matrix. Therefore, the homogenization treatment at the temperature of about 460 ℃ can make up the defects, the specific heat treatment process scheme is shown in table 1, and the final scheme is finally determined through physical and chemical property inspection and durability test.

Table 1: different heat treatment process examples.

1.1 metallographic structure

Sampling a product body, cooling the product body at 535 ℃/8H along with a furnace by T6 heat treatment, wherein eutectic silicon is fine and has a needle-shaped eutectic silicon tissue, and the distribution of the eutectic silicon is not uniform, which is shown in figure 1; the high-power structure of the heat treatment process of air cooling T6 at 260 ℃ with furnace cooling at 545 ℃/10H is characterized in that eutectic silicon is in a point-like and short rod-like structure, the high-power structure of air cooling T6 at 260 ℃ with furnace cooling at 460 ℃/6H +545 ℃/12H is fine and is distributed along a dendritic crystal network, as shown in figure 2, eutectic silicon can be seen to be in a short rod-like shape and not well degenerated from the high-power structure of various heat treatment processes, and harmful phases such as blocky primary crystal silicon, a needle-like iron phase and needle-like AlMnFe are not found.

1.2, mechanical properties

Sampling of a product body, and meeting the performance requirement: the test results of Rm is more than or equal to 216MPa, Rp0.2 is more than or equal to 152MPa, and A is more than or equal to 3.5 percent are shown in the following table 2.

TABLE 2 mechanical Property test results

From the test data: the strength of the new T6 treatment is not changed greatly from that of the normal T6 treatment, the yield strength is reduced by 20MPa, the elongation is improved by 63%, after the homogenization treatment is adopted, the strength and the plasticity of the product are improved to some extent, but the change of the alloy strength is not large by adopting a 550 ℃/10-12H air cooling homogenization process, the plasticity ratio is improved by 62.8% after the new T6 treatment, and the strength of the alloy is improved by 20MPa and the plasticity is improved by 23% by adopting a furnace-cooling homogenization and T6 treatment process compared with the 550 ℃/10-12H air cooling homogenization and T6 process, the air cooling homogenization and T6 treatment process is carried out when the temperature of 545 ℃/10H is cooled to 260 ℃ along with the furnace, but the elongation is 2.62%, and the requirement cannot be met.

And under the process of double homogenization (air cooling after cooling to 260 ℃ along with the furnace at 460 +/-5 ℃/6H +545 +/-5 ℃/12H) + T6 treatment, the alloy strength is improved by 20MPa compared with the strength of the T6 heat treatment again, the elongation is improved by 183 percent, the strength of the double homogenization + T6 treatment is basically consistent compared with the strength of the single homogenization + T6 treatment alloy, but the elongation is improved by 39.6 percent and is 3.66 percent. The product performance requirement can be met by adopting the technology of cooling to 260 ℃ along with the furnace at 460 plus or minus 5 ℃/6H plus or minus 545 plus or minus 5 ℃/12H, then air cooling and then T6.

1.3 fatigue test

The product is cooled to 260 ℃ along with the furnace at the temperature of 460 ℃/6H +545 ℃/12H, then air-cooled, and subjected to the T6 (quenching 538 ℃/6H aging 155 ℃/4H) process to carry out the endurance test, wherein the test requirements are as follows: the loading force is 4.5KN, and the circulation is 100 ten thousand times. The practical result is as follows: the fracture was not broken by 7KN/100 ten thousand times, 8KN/100 ten thousand times, 9KN/100 ten thousand times, and 10KN/100 ten thousand times. The safety factor is increased by 2 times, and the product has no defects such as fracture and the like.

In a word, the intensity and the plasticity of the alloy can be improved by adopting homogenization treatment, and the plasticity of the alloy is better by adopting double homogenization + T6 treatment than single homogenization + T6 treatment.

2. For alloys with high requirements for the AlSi7Mg0.3(a) material, the bulk property requirements are: the performance and the metallographic phase are compared by adopting the conventional T6 treatment (538 ℃/6H aging 155 ℃/4H for quenching) and the homogenization treatment (460 ℃/6H +545 ℃/12H for furnace cooling to 260 ℃) and then air cooling) + T6 (538 ℃/6H aging 155 ℃/4H for quenching).

2.1 metallographic structure

The high-power structure eutectic silicon is fine, the aggregation phenomenon is not obvious, the eutectic silicon is in a dot shape and a worm shape, the passivation effect is good, the deterioration is normal, and the figure is 3.

2.2, performance test results:

sampling of a product body, and meeting the performance requirement: rm is more than or equal to 224Mpa, Rp0.2 is more than or equal to 152Mpa, A is more than or equal to 5 percent, and the test results are shown in the following table 3.

TABLE 3 AlSi7Mg0.3(a) test results (product bulk sample)

The test results show that the strength of the direct T6 treatment is improved by 30MPa and the elongation is improved by two times by adopting the invention, namely, the strength of the direct T6 treatment is improved by air cooling after cooling to 260 ℃ along with the furnace at 460 ℃/6H +545 ℃/12H, and then the strength of the direct T6 treatment is improved by 155 ℃/4H after quenching 538 ℃/6H, and all indexes can meet the product performance requirements.

The process of the invention adopts homogenization (460 ℃/6H +545 ℃/12H is cooled to 260 ℃ along with the furnace and then is air-cooled) + T6 (538 ℃/6H aging 155 ℃/4H is quenched) to improve the strength and plasticity, especially the plasticity of the alloy, and can bring the maximum potential of the alloy into play.

In conclusion, the two cases are enough to show that the invention can completely solve the problem that the strength and the plasticity can not meet the product requirements due to insufficient structure refinement and deterioration, and the invention is also a good reworking treatment for the problem, so that the cost can be saved, and the maximum potential of the alloy can be excavated.

The invention has the advantages and positive significance that:

1. the double homogenization and T6 heat treatment is adopted, the effect is better than that of single homogenization and conventional T6 treatment, mainly the homogenization of 460 ℃/6H can ensure that the compound which is extremely dissolved into the basic alloy in the casting process is uniformly precipitated, then the 545 ℃/12H treatment is carried out to ensure that the strengthening phase (Mg2Si) and the Si phase are uniformly distributed, all the compounds are uniformly dissolved into the matrix, and then the matrix is cooled along with the furnace, the compound is uniformly precipitated, and the plasticity of the alloy can be greatly improved.

2. The homogenization treatment is applied to the cast aluminum alloy, so that the strength and the plasticity of the alloy can be improved, particularly the plasticity is obviously improved by about 2 times, and a thought is provided for researching the cast aluminum alloy with high strength and plasticity.

In summary, the present invention is only a preferred embodiment, and is not intended to limit the scope of the invention, i.e. all equivalent changes and modifications made according to the content of the claims of the present invention should be considered as the technical scope of the present invention.