Microstructure and Mechanical Properties of Aluminum Alloy with Ultra-high Strength Prepared by Spray Forming

Abstract

In this paper, Al–11Zn–3Mg–2Cu–0.2Zr alloy was prepared by spray-forming, and then it was treated by defect reduction, hot worked and heat treatment. Microstructure and mechanical properties of the aluminum alloy were researched during the whole processing by metallographic microscope, scanning electron microscope (SEM), and tensile test. Average grain size of spray-formed aluminum alloy was about 10–20 μm due to the high cooling rate closing 1000 K/s, and shrinkage porosity and cavity was inevitable in spray-formed ingot because of nitrogen as carrier. Through hot isostatic pressing and hot extrusion, the relative density increased from 87– 90% to almost 99–100%, but it decreased again to about 98% after solution, which meant some porous defects could not be eliminated thoroughly. Comparing with casting, the original grain of spray-formed ingot was much smaller, which was unsuited for plastic processing with large deformation. A large plastic deformation caused lots of recrystallization, which weakened the mechanical properties. In the areas without defects, the best properties of the spray-formed alloy were 825 MPa in tensile strength, 808 MPa in yield strength, and 9% in elongation.