Effects of welding chamber height on properties of porthole die extrudates made of 0.5 wt.% GNPs/Al composite

In this study, porthole die extrusion was first performed on a 0.5 wt% GNP-nanoplatelet-reinforced aluminium matrix composite by using welding chambers having heights of 10, 15, and 20 mm. The effects of the welding chamber height on the microstructure and mechanical properties of the composite in the welding zone were studied. The observation results show that there are no macroscopic defects in the interface of the extrudate by the die with different welding chamber heights. The welding degree and ductility of the longitudinal weld of the extrudate increase with the increase of the height of the welding chamber. When the welding chamber height was 20 mm, the comprehensive mechanical properties of the composite along the extrusion direction and the vertical direction were the best. This was mainly because a higher hydrostatic pressure and shear force in the welding chamber with the height of 20 mm increased the recrystallisation degree of the composite, resulting in smaller sizes and an even distribution of the GNP and alumina nanoparticles inside the grain, which played positive role in hindering the dislocation slip. Further, the interface strength between GNP and the matrix was also enhanced characterized by the light and sharp tearing edge in the tensile fractography. The presence of GNP hindered the closure of micro-holes in the weld, and an increase in the welding chamber height effectively reduced the size of micro-holes, thereby improving the welding quality. So larger welding chamber height should be recommended without sacrificing stability and life of the die.