Effects of Ingot Casting Pre-Precipitation Treatment on the Microstructure and Properties of Al-4.3Zn-1.7Mg Alloy

The effects of the single-stage homogenization process without pre-precipitation treatment and the two-stage homogenization process with pre-precipitation treatment on the microstructure and mechanical properties of Al-4.3Zn-1.7Mg alloy were investigated contrastively by optical microscopy (OM), scanning electron microcopy (SEM), transmission electron microcopy (TEM) and uniaxial tension (TS) test. The results show that the trace elements Mn, Cr and Zr in the alloy after semicontinuous casting quenching are retained in the form of solid solution in the matrix, and the pre-precipitated phase particle Al6Mn, Al7Cr and Al3Zr are precipitated in the process of homogenization treatment for supersaturation solid solution. The precipitation behavior of the precipitated phase can be improved significantly in the process of homogenization by the low temperature pre-precipitation treatment. The fine pre-precipitated phase with dispersion distribution is obtained. The precipitated phase particles have good thermal stability, and they cannot be markedly coarsened in the process of hot rolling and subsequent solid solution aging heat treatment. So the migration of grain boundary and dislocation movement are inhibited significantly, and the performance of alloy plate is improved.