Resistance spot welding of ultrafine grained/nanostructured Al 6061 alloy produced by cryorolling process and evaluation of weldment properties

Resistance spot welding process was used to produce ultrafine grained/nanostructured Al 6061 alloy joints. In this regard, ultrafine grained/nanostructured 6061 aluminum sheets were first produced by cryorolling and then joined by resistance spot welding. For this purpose, the samples were solution treated at 530 °C for 3 h and subsequently cryorolled up to 90% reduction in thickness. In order to improve strength and ductility, the cryorolled sheets were then subjected to ageing treatment. The average size of fine grains of the peak aged alloy reached to ∼60 nm. In peak aged condition, an ultimate tensile strength of 365 MPa, a hardness of ∼140 HV and a ductility of 11.8% was obtained. The cryorolled, peak aged, and also 6061-T6 Al alloy sheets (witness samples) were then resistance spot welded. Results showed that the cryorolling process can effectively increase the electrical resistivity of Al 6061 alloy. From tensile-shear tests, the highest peak load of spot welds was obtained for the cryorolled specimens. This is due to higher electrical resistivity of the cryorolled samples which increases the nugget diameter and therefore the peak load of the spot welds. A decrease in microhardness was observed in the fusion zone due to dissolution of Mg2Si strengthening precipitates in this region during welding process.