Study on the solid solution temperature of achieving ultra-high strength in wire-arc additive manufactured Al-Zn-Mg-Cu aluminum alloy

Al-Zn-Mg-Cu aluminum alloys are typically heat-treatable aluminum alloys. The heat treatment has a significant effect on the microstructure and mechanical properties of Al-Zn-Mg-Cu alloy. In this study, the solid solution temperature of achieving ultra-high strength in wire-arc additive manufactured 7B55 aluminum alloy was sys-tematically investigated. The results showed that the microstructure of the as-deposited 7B55 aluminum alloy was composed of equiaxed grains with an average grain size of 4.2 +/- 0.5 mu m. A large number of the second phases were continuously distributed along grain boundaries. The precipitated phases within grains were mainly composed of the larger eta phases and the smaller eta ' phases, and the amount of precipitated phases was fewer. The second phases distributed along grain boundaries gradually dissolved into alpha-Al matrix with the increase of solid solution temperature, resulting in a higher supersaturation of the alpha-Al matrix and more homogeneous distri-bution of alloy elements. Combined with the results of DSC analysis, the optimal solid solution temperature of the 7B55 aluminum alloy was determined to be 480 degrees C. After solid solution of 480 degrees C,the microstructure was still composed of equiaxed grains with an average grain size of 4.8 +/- 0.4 mu m. The size of the grain did not grow significantly. A larger number of nanoscale fine GP zones, eta ' phases and secondary Al3(Sc,Zr) particles were precipitated within the grains during subsequently artificial aging process, resulting in a significant increase in tensile properties. The ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) reached 621 MPa, 555 MPa and 5.73%, respectively, which was significantly higher than the strength level of WAAM aluminum alloy reported among all the existing literature.