MICROSTRUCTURAL ANALYSIS OF Al-Mg-Si-Zn ALLOY

As a part of an overall effort to develop a new Al-alloy appropriated for structural applications, a characterization research was directed towards the development of microstructure and their relationship with heat treatment. The Al-Mg-Si-Zn was chose for that purpose due to the presence of precipitates in alpha-Al matrix and at grain boundaries, capable to get an excellent relationship between hardness and mechanical resistance. With regards to microstructure, this was characterized in the as-cast and as-aged condition. This treatment was carried out in two stages, the first one at 450 degrees C during 3 hr which correspond to homogenization treatment and the second one, the ageing treatment at 160 degrees C 1hr. Results of microstructure characterization in the as-cast ingots showed the alpha-Al dendrites, and in addition the presence of a binary eutectic and particles of Mg7Zn3 type in interdendritic regions. The eutectic and particles were modified by the aged treatment. Transmission electron microscopic observations carried out in specimens with and without heat treatments showed a uniform distribution of precipitates with different morphologies like cubic, spherical and platelet; in the matrix, which were no detected during the scanning electron microscope observations.