Effects of billet heating temperature and extrusion speed on the microstructures and mechanical properties of the longitudinal welds in aluminum alloy profiles with complex cross-section

Abstract

The effects of billet heating temperature and extrusion speed on the microstructures and mechanical properties of longitudinal welds in the aluminum alloy profiles with complex cross-section were studied. The results show that as the billet heating temperature or extrusion speed gradually increases, the average grain size shows a decreasing trend, the average grain boundary misorientation angle shows an increasing trend, and the density of dislocations increases first and then decreases. The elongation (EL) shows a trend of increasing first and then decreasing. Higher billet heating temperature contributes to increase the ultimate tensile strength (UTS) and yield strength (YS) of the longitudinal welds, while extrusion speed has little effect. Poor welding quality is the main factor leading to the low mechanical properties of the longitudinal welds. When the welding quality is higher, the interaction between dislocations and precipitation phases has an important impact on the mechanical properties of the longitudinal welds. The longitudinal welds of the profiles studied in this work have the highest EL and the largest UTS when the combinations of the billet heating temperature and the extrusion speed are 490 °C × 3.5 mm/s and 520 °C × 3.5 mm/s, respectively.