Interfacial bonding mechanism and length evaluation method of the longitudinal welds in the unsteady deformation process of porthole die extrusion of aluminum alloy profiles

Abstract

In this work, a porthole die extrusion experiment was carried out on an aluminum alloy profile used for air-conditioning refrigerator ice box. Microstructural characterization and mechanical property tests were performed at different positions of a longitudinal weld in the profile head. The results indicated that, from the unsteady to steady extrusion stage, the number, sizes and depths of the voids gradually decrease. The oxides are gradually broken into flakes and eventually disappear. The grain boundaries gradually cross the welding interfaces to form new grains, and the welding quality is gradually improved. The ultimate tensile strength (UTS) of the longitudinal welds shows an upward trend, the elongation (EL) first rises and then tends to be stable. Before complete welding, the hardness at the welding interface is lower than those of the areas on both sides of the interface. Based on the results of testing and characterization, the interfacial bonding mechanism of the longitudinal welds in the unsteady zones was revealed. A method for predicting the length of the unsteady zones of profiles extruded by porthole die was proposed, by which the length of the unsteady zone of the aluminum alloy profile used for air-conditioning refrigerator ice box was successfully predicted.