Microstructural and mechanical characterization of various modified 7XXX series spray formed alloys

Microstructural analysis was conducted on the second phase constituent particles in various modified 7XXX series alloys produced by spray forming. High gas-to-metal ratios of 4.45, as opposed to low gas-to-metal ratios of 1.95, were found to produce a more refined grain structure with an evenly distributed second phase. To elucidate the influence of Zn, Cr, Cu and Zr additions on the microstructure, five different alloy compositions were chosen. The microstructure after extrusion and aging was studied using optical, scanning and transmission electron microscopy. The coarse constituent particles were found to be Al6(MnFe) and Al7Cu2Fe. Two different types of dispersoids were identified; fine, of the L12 type (Al3Zr) and larger dispersoids of the Al18Mg3Cr2 compound referred to as the E-Phase. Room temperature mechanical properties of spray formed Al-Zn-Mg-Cu alloys were investigated in the T6 and T7 aged condition. Variations in structural particle concentration were found based on aging and composition type.