Enhancing strength, ductility, and fatigue performance of Al-Zn-Mg-Cu-Sc-Zr alloy using a hybrid approach: Wire-arc directed energy deposition and interlayer friction stir processing

Porosity defects are the main issues faced by aluminum alloys manufactured by wire-arc directed energy deposition (WA-DED), which seriously affect the mechanical properties of WA-DED aluminum alloys, especially the fatigue properties. Thus far, there is still no effective solution for the elimination of porosity in high-strength WA-DED aluminium alloys. In this study, an innovative hybrid WA-DED + interlayer friction stir processing (FSP) method was applied to successfully fabricate thick-walled Al-Zn-Mg-Cu-Sc-Zr aluminum alloy component with enhanced strength-ductility and fatigue properties by utilizing a custom 7B55-Sc wire. The porosity defects caused by the WA-DED process were significantly reduced in the FSP effective zone, and the original continuous grain boundary eutectic structures were broken up and dispersed along the grain boundaries. The grains were also further refined with an average size of about 1.1 ± 0.2 μm in the stirring zone (SZ) and 1.6 ± 0.3 μm in the overlapping SZ. The nanoscale intragranular precipitates (IGPs) were mostly composed of both rod-like ηMg(Zn,Cu,Al)2 phases and secondary Al3(Sc, Zr) phases. The yield strength (YS), ultimate tensile strength (UTS) and uniform elongation (EL) in the horizontal and vertical directions were all substantially improved comparing with the WA-DED 7B55-Sc component, especially in the horizontal direction, reaching 387 ± 7 MPa, 511 ± 15 MPa and 14.6 ± 0.5%, respectively. The fatigue property after 1 × 107 cycles for the WA-DED + interlayer FSP 7B55-Sc sample was significantly increased by 81%, reaching 170 MPa in vertical direction compared to 100 MPa of the WA-DED 7B55-Sc component.