Depositing Al–Zn–Mg–Cu alloy with different positive electrode/negative electrode ratios of CMT advance process

Abstract

To explore the influence of electrode positive/electrode negative (EP/EN) ratio on the CMT advance-based wire arc additive manufacturing (WAAM) process for Al–Zn–Mg–Cu alloy, the behaviors of the deposition process, the microstructure and mechanical properties of Al–Zn–Mg–Cu alloy WAAM are studied. The results showed that electrical waveforms and arc/metal transfer were unstable with a low EP/EN ratio, which deteriorated the stability of WAAM. The forming accuracy of deposited samples firstly increased with the EP/EN ratio ranging from 4:16 to 13:7 and then decreased if the EP/EN ratio continued increasing. In the inter-layer region, the samples showed a combination of columnar grains and pony-size equiaxed grains with an EP/EN ratio ranging from 4:16 to 10:10, while the size and quantity of equiaxed grains increased and the columnar grains almost disappeared with a higher EP/EN ratio (≥ 13:7). The enriched alloy elements in the grain boundary were easy to form large-scale precipitated phases, which were harmful to the mechanical properties. The microhardness distribution of all samples had the apparent fluctuation along the building direction due to the existence of the microstructure evolution and pores defect. This study proved that the CMT advance process was a practicable and effective way for improving the performances of Al–Zn–Mg–Cu WAAM components with optimal EP/EN ratio.