Study On Heat Treatment Process And Superplasticity Of 7475 Alloy By Spray Forming

In this paper, the microstructure and properties of as-deposited and as-extruded 7475 alloys processed by spray forming, the effect of heat treatment on the microstructure and properties and the superplasticity of as-extruded 7475 alloy were studied by using such research means as optical microscopy, X-ray diffraction, SEM, TEM and EDS, and through different performance tests. The main results are showed as follows:A large-scale 7475 Aluminum alloy billet with a size ofФ360 mm×1200 mm was successfully prepared by spray forming. The typical microstructure is composed of homogeneous equiaxed grains with the size between 30μm and 50μm. There is no macro-segregation and the density gets up to 97%.σb of as-deposited 7475 alloy got up to 245.7MPa, andδwas 5.85%. After extrusion, the pores were eliminated and the second-phases were more homogeneously distributed. After extrusion, the tensile strength and elongation increased. Compared to alloy by casting, the strength and elongation increased 45.5% and 25.3% respectively.The optimal single-stage solution temperature for spray-formed 7475 alloy is 480℃, and the proper solution time is 3h. Double-stage solution and aging can increase the strength, but reduce the elongation.After single-stage peak aging,σb got up to 738MPa,δwas 9.0%. Compared to the alloy by casting, the strength and elongation increased by 33% and 12.5% respectively.With the increase of second-stage aging temperature and extension of aging time, the strength reduces, but the elongation and conductivity increases.RRA treatment could get excellent comprehensive properties. After RRA treatment,σb got up to 716MPa,δwas 10.3% and the conductivity was 43.3%IACS.An elongation of 960% was got at 516℃and the strain rate of 8.33×10-4 s-1 after superplastic tensile tests on as-extruded 7475 alloy after recrystallization.