Effect of the T6 Heat Treatment on Microhardness of a Directionally Solidified Aluminum-Based 319 Alloy

Aluminum alloys of the ANSI series 319 present Si and Cu as the main alloying elements and the mechanical strength of these alloys can be improved by the precipitation of the metastable Al2Cu phase during the ageing heat treatment. In this paper, the Al-5.5wt.%Si-3wt.%Cu alloy was elaborated and solidified in a water-cooled horizontal directional solidification device. The as-cast ingot was subjected to the precipitation hardening heat treatment (T6 heat treatment), which consisted of: solution for 5 h at 490°C±2°C, followed by quenching in water at 60°C±2°C and ageing for 3 h at 155°C±2°C, and cooling-air. Secondary dendrite arm spacing (λ2) measurements were carried out before and after T6 heat treatment. The mechanical strength of the alloy was investigated by the microhardness test. It has been found that the heat treatment did not influence the λ2 values, however, highest HV values have been observed for the heat-treated samples.

ANSI系列319铝合金以硅（Si）、铜（Cu）作为主要合金元素，该类合金的力学强度可通过时效热处理过程中亚稳态Al₂Cu相的析出得到提升。本文制备了Al-5.5wt.%Si-3wt.%Cu合金，并采用水冷式水平定向凝固装置完成凝固成型。对铸态锭坯实施析出强化热处理（T6热处理），其工艺为：在490℃±2℃下固溶处理5小时，随后于60℃±2℃的水中淬火，接着在155℃±2℃下时效3小时，最后采用空冷方式冷却。分别在T6热处理前后开展了二次枝晶臂间距（secondary dendrite arm spacing, λ2）的测量。通过显微硬度试验对该合金的力学强度进行了研究。结果表明，热处理对二次枝晶臂间距λ2的数值无影响，但经热处理后的试样的维氏硬度（Vickers Hardness, HV）值达到最高。