Porosity evolution mechanisms, influencing factors, and ultrasonic-assisted regulation in joining high Mg-content aluminum alloys

Abstract

Over the years, porosity defects have been one of the significant factors limiting the development of aluminum alloys during the joining process. This paper employs the process of laser metal deposition welding (LMDW) to join Al-Mg-Sc-Zr alloys with high Mg content. Through the micromorphology of pores, elemental distribution, and finite element analysis (FEA), the mechanisms of formation, growth, and spillage of pore defects in aluminum alloys containing low-melting-point elements are explored. This study not only delves into the mechanism of low-melting-point element-induced porosity and enriches the principle of porosity formation, but also explores the influence of heat transfer paths and flow fields on the porosity enrichment during the butt-welding process, which provides a reference direction for future research. The study examines the effects of different process parameters and layers on the distribution and size of pores, revealing that pore-rich areas are concentrated along the fusion lines and the interlayer fusion lines. Furthermore, the three-dimensional model is constructed via finite element analysis to simulate the distribution of Mg and the flow field within the melt pool. Finally, ultrasonic vibration is introduced to mitigate porosity defects. Through controlled experiments, the optimal ultrasonic vibration current parameters are identified that minimize Mg loss and alleviate pore accumulation along the fusion lines and interlayer fusion lines. Compared with no ultrasonic vibration, the porosity at the melt pool center ameliorated by 20 %, the porosity near the fusion line decreased by 22 %, and the tensile strength increased by 41.9 %.