Effects of heat treatment and addition of small amounts of Cu and Mg on the microstructure and mechanical properties of Al-Si-Cu and Al-Si-Mg cast alloys

The present study investigates the effects of heat treatment on the microstructures and mechanical properties of Al-Si-Cu and Al-Si-Mg alloys containing small amounts of added copper and magnesium, with the aim of obtaining the maximum alloy hardness via the adjustment of the solution heat treatment and aging. The solution heat treatment was performed at 500 degrees C and 525 degrees C for the Al-Si-Cu alloy and at 525 degrees C for the Al-Si-Mg alloy. The samples of both alloys were solution treated for various times between 5 min and 16 h, followed by quenching and finally an artificial aging was performed at 210 degrees C for a time ranging from 10 min to 50 h. The microstructures of the as-cast alloys and heat-treated samples were studied using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and hardness tests. The results show that the solution treatment time significantly affects the coarseness of the microstructure, causes the dissolution of the intermetallic phases, and homogenizes the distribution of copper and magnesium in the matrix. The peak-aged Al-Si-Cu alloy was obtained after a solution heat treatment at 525 degrees C for 15 min followed by 2 h of aging. The peak-aged Al-Si-Mg alloy was obtained after 8 h of solution heat treatment at 525 degrees C followed by 40 min of aging. The Al-SiMg alloy with the 0.6 wt% Mg addition displayed an age-hardening response that was approximately 34% higher than that of the Al-Si-Cu alloy with a 0.3 wt% Cu addition. (C) 2018 Published by Elsevier B.V.