Microstructure Analysis on 6061 Aluminum Alloy after Casting and Diffuses Annealing Process

One factory using semi-continuous casting process produce the phi 200x6000mm 6061 aluminium alloy barstock, and then rotary forged for car wheels. 6061 distorting aluminium alloy is an forged aluminum alloy, and mainly containing Mg, Si, Cu and other alloying elements. The main strengthening phase is Mg2Si, and also has few phase of (FeMn) 3Si2Al15. In order to eliminate the segregation and separation which present in the crystal boundary, and make the distortion to be uniform, and does not present ear and fracture defects after the forging. So the 6061 distorting aluminium alloy adopt the diffusion annealing heat treatment before the forging process. According to the current conditions, we use the diffusion annealing which have the different heating temperature and different holding time. The best process we can obtain from the test which can improve the production efficiency and reduce the material waste, improve the mechanical properties, and eliminate the overheated film on the surface. Then, we using OM, SEM and EDS to analyse the microstructure and the chemical composition of compound between the surface and centre. The result shows that the amount of segregation were different in the surface and in the center, and the different diffusion annealing can cause the phase change in the surface and the center. (C) 2013 The Authors. Published by Elsevier B.V. Open access under CC BY-NC-ND license.