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ã€China Aluminum Industry Network】 Casting aluminum alloy heat treatment usually adopts solution treatment and aging treatment. During solution treatment, it is heated to a certain temperature and then cooled (water-cooled) to obtain a solid solution with a certain degree of supersaturation, and the mechanical properties of the alloy are improved by aging strengthening. In recent years, deep cryogenic treatment of aluminum alloys has also been studied, and it has been demonstrated that the alloy mechanical properties can be improved. Aluminum alloy cryogenic treatment process is relatively single, usually solid solution heating water cooling to room temperature before cryogenic treatment, and subsequent aging treatment. This paper will cast aluminum alloy solution heat after heating and cooling directly in liquid nitrogen and heat for a certain period of time, that is to say, the water cooling process and cryogenic treatment process will be combined into one process, which is called "solid solution cryogenic treatment". By testing the changes in the mechanical properties of the alloy, a better heat treatment strengthening method for the cast aluminum alloy is sought.
The experimental materials were self-made ZL alloys, ZL101 and ZL109 cast aluminum alloys. Self-made ZL alloy samples were cast in the laboratory and the components (mass fraction, %) were: 7.0Si, 1.0Mg, 92Al. The cryogenic treatment medium is the industrial liquid nitrogen (-196°C) provided by the oxygen plant. Three cast aluminum alloys are processed using the following three processes:
1 solution treatment (water cooling) + aging;
22 solution treatment (water cooling) + liquid nitrogen cryogenic 48h + aging;
33 solution heat after heating and direct liquid nitrogen cryogenic 48h + aging. In order to understand the effect of cryogenic treatment on aging performance, in addition to the above-mentioned artificial aging, some of the samples were also subjected to natural aging for 75 days, and their hardness changes were tested.
The cryogenic treatment of Al-Si-based alloys increases the hardness and strength, and has a significant strengthening effect. Some cryogenic treatment processes can also maintain plasticity and have a strengthening and toughening effect. The effect of solid solution cryogenic treatment on the mechanical properties of Al-Si alloy is better than that of conventional cryogenic treatment. Cryogenic treatment has a pre-aging effect on Al-Si alloys, promotes the uniform dispersion of the second phase, and is beneficial to the improvement of mechanical properties.