Analysis of the effects of solution heat treatment and artificial aging on the microstructure of aluminum alloy A356

ABSTRACT

The present study investigated the effects of solution heat treatment and artificial aging (T6) on the microstructure of the A356 (Al7Si0.3Mg) aluminum alloy. To characterize the results, micro hardness test and techniques of light and electron microscopy were used. Samples of the A356 alloy casting, with distinct weight percent of Mg (0.28, 0.38 and 1%Mg), were solubilized for 10h at 5400 C and subjected to different temperatures and times of artificial aging. The results showed that the hardness rises with increasing aging temperature, but exhibits a sharp drop in samples exposed to higher temperatures (2150 C). Regarding aging time, increments were observed in the hardness values for the use of higher aging times. In order to identify microstructural changes associated with modifications in mechanical properties and to identify the mechanisms involved, analyzes were performed by optical microscopy, scanning and transmission electron microscopy. Significant changes in the microstructure and the hardening of the alloy matrix were found, as a function of increasing additions of magnesium. However, the microstructural phenomena associated with precipitation hardening were only detected by using transmission electron microscopy, which showed the presence of nano precipitates responsible for precipitation hardening as well as precipitates incoherent with the matrix, thus indicating the occurrence of overaging.

Keywords:
heat treatments; aluminum alloys; precipitation hardening; transmission electron microscopy