Influence of solute Mg and Zener–Hollomon parameter on microstructural evolution of linear-friction-welded Al joints

Abstract

Linear friction welding (LFW) was performed on face-centered cubic materials, that is, Al alloys (AA1050 and AA5052) with different stacking fault energies (SFEs). The pressure was controlled during the LFW to clarify the effects of temperature, strain, and strain rate on microstructural evolution and dynamic recrystallization (DRX) mechanism. The microstructural evolution during DRX was mainly dependent on the temperature. The grain structures and textural evolution at high temperatures were governed by a continuous DRX, whereas those at low temperatures were primarily controlled by a discontinuous DRX. Various parameters determined the grain structure and textural evolution in different regimes. The evolution of grain structures and texture was dominated by strains and strain rates at temperatures above 0.5Tm (Tm: melting temperature) and by the SFE at temperatures below 0.5Tm. The Zener–Hollomon parameters of the Al alloy joints were investigated. It was found that the slope in AA5052 is larger than that in AA1050 during LFW. At a lower Z value, the grain diameter of the AA5052 joints was larger than that of the AA1050 joints, presumably because of the lower strain rate. Contrastingly, at a higher Z value, the grain diameter of the AA5052 joints was smaller than that of the AA1050 joints, even though the strain rates of the AA5052 joints were considerably lower than those of the AA1050 joints. These results were mainly attributed to the lower SFE of AA5052, which promoted DRX and grain refinement during the LFW. This report reveals the effects of SFE, temperature, strain, and strain rate on the DRX-induced microstructural evolutions during severe plastic deformation.