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 degrees C +/- 2 degrees C, followed by quenching in water at 60 degrees C +/- 2 degrees C and ageing for 3 h at 155 degrees C +/- 2 degrees C, and cooling-air. Secondary dendrite arm spacing (lambda(2)) 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 lambda(2) values, however, highest HV values have been observed for the heat-treated samples.