TWI Industrial Member Report Summary 727/2001
A J Leonard
Background
Friction stir welding has become commercially viable in the joining of aluminium alloys and this group of materials has been the basis of many studies on the process. However, the research to date has largely concentrated on process development and the understanding of mechanical properties. Only a limited number of corrosion studies has been performed, despite the fact that potential applications require an understanding of environmental degradation.
Previous TWI work reported on the resistance of friction stir welds in alloy 2014A-T651 to both intergranular and exfoliation corrosion. Similar tests were also performed on friction stir welds in alloy 7075-T651, which had received a postweld retrogression and re-ageing heat treatment. Exfoliation corrosion tests on welds in alloy 2014A-T651 demonstrated that the resistance of the weld was similar to that of the parent metal, although slightly greater attack did occur in the heat affected zone. Both the weld and parent metal were susceptible to intergranular corrosion. Tests performed on welds in 7075-T651 after postweld heat treatment (PWHT) revealed that the weld was susceptible to exfoliation corrosion, to a greater extent than the parent metal. However, neither the parent metal nor weld was susceptible to intergranular corrosion.
The current work formed part of an integrated TWI assessment of microstructure, fracture toughness and corrosion resistance of friction stir welds in two aluminium alloys: an Al-Cu-Si-Mg alloy, 2014-T651 and an Al-Zn-Mg-Cu alloy, 7075-T651.
Objective
- To determine the corrosion performance of friction stir welds in two aluminium alloys.