Wire arc additive manufacturing of components using TiC/Ti reinforced Al-Zn-Mg-Cu alloy wire: Microstructure evolution, strengthening mechanism, and fracture behavior

This study addresses the challenges of uneven microstructure and hot cracking in wire arc additive manufacturing (WAAM) Al-Zn-Mg-Cu alloy, and the crack-free high-performance components were successfully prepared using cold metal transfer-based WAAM with TiC/Ti reinforced Al-Zn-Mg-Cu alloy wire. The results indicate that the microstructure of the as-deposited and T6 heat-treated samples comprises fine equiaxial grains, with an average size of approximately 8-9 mu m. The grain refinement is mainly dependent on the heterogeneous nucleation of L12-Al3Ti phase, the constitutional supercooling zone formed by the Ti element, and the physical blocking growth layer of TiC particles. Compared to the as-deposited sample, the ultimate tensile strength of the T6 heat-treated sample in the horizontal direction reached 578.5 +/- 5.6 MPa (an increase of 49.3 %), and the elongation was 6.4 +/- 0.3 % (a decrease of 13.5 %). It is found that the high mechanical properties of the T6 heattreated samples are mainly attributed to the combined effects of fine grain strengthening (67.1 MPa), solid solution strengthening (60.6 MPa) and precipitation strengthening (339.1 MPa). Additionally, both the asdeposited and T6 heat-treated samples presented a mixed fracture model, with cracks initiating at the brittle hard phase(L12-Al3Ti and Al18Mg3Ti2) and grain boundary, and then primarily propagating along the grain boundary.