Significant grain refinement and enhanced mechanical properties of 6070 Al alloy via Ti/Sr addition and hot extrusion

The effects of Al-5Ti-1B and Al-10Sr master alloys on the microstructure and tensile properties of extruded 6070 Al alloy have been investigated in current research. Different amounts of Al-5Ti-1B and Al-10Sr master alloys were added to provide 0.01-0.5 wt.% of each element (Ti/Sr) in the alloy before homogenization, extrusion and heat treatment process. After adding 0.03 wt.% Ti and 0.03 wt.% Sr to the alloy separately, reduction in the average grain size was found to be %83 and eutectic Si changed from needle shape to fine fibrous morphology. Although the combined addition of Al-5Ti-1B and Al-10Sr increased slightly the grain size of the alloy, there was a considerable improvement in tensile properties for the extruded and T6-heat treated specimens. Further improvement in tensile strength was achieved after T6 heat treatment for 0.1 wt% Sr + 0.03% Ti added specimens in which ultimate tensile strength (UTS) showed the highest value (410 MPa). Fracture surface examinations revealed that hot extrusion process changes the mode of fracture from brittle in the as-cast condition to a more ductile form.