Design and cracking susceptibility of additively manufactured Al-Cu-Mg alloys with tandem wires and pulsed arc

Experimental investigations on cracking susceptibility were carried out for wire + arc additively manufactured (WAAM) Al-Cu-Mg alloys, which were designed and deposited with Al-Cu and Al-Mg wires in tandem. The influence of composition, heat input, mechanical properties and microstructure on cracking for ternary WAAM Al-Cu-Mg alloys were studied, aiming at minimizing cracks during deposition. Both macro and micro cracks were observed and identified to be inter-granular solidification cracks. The contour map of cracking susceptibility as functions of Cu and Mg contents was constructed, revealing that the composition range within Cu 4.2%-6.3% and Mg 0.8%-1.5% is less susceptible to cracks during solidification terminating in an isothermal ternary eutectic reaction. Higher micro hardness generally reduces the cracking susceptibility. Contour maps about thermal effects during deposition indicate higher wire feed speed causes higher heat input but lower density for deposited alloys, remarkably increasing solidification cracks. Peak susceptibility appears when micro hardness is lower than 95 HV and heat input is greater than 200 J/mm. Micro cracks may initiate from the inter-layer equiaxed grains zone for WAAM alloys if insufficient liquid feeding dominates during deposition. The proposed model can predict solidification cracking tendency for WAAM Al-Cu-Mg alloys.