Analysis of AA 6082-T6 welds strength mismatch: stress versus hardness relationships

In current work, linear stress-hardness relationships are established, relating the hardness in different AA 6082-T6 weld zones with local tensile properties. The welds were performed by friction stir welding (FSW), using varying welding parameters, in order to obtain a diversified range of weld mismatch conditions. Local tensile properties for the thermo-mechanical-affected zone (TMAZ) and heat-affected zone (HAZ) were assessed from tensile testing of transverse samples using digital image correlation (DIC). The proposed stress-hardness relationships, which relate hardness with yield strength and flow stress, at different plastic deformation values, are suitable to be used for assessing plastic properties, from hardness data, for AA 6082 alloys, in the naturally aged and overaged conditions, characteristic of different weld zones of any type of welds in this aluminium alloy. The evolution of friction stir welds' local and global tensile properties, with varying welding parameters, is also analysed. It is shown that in spite of the large scatter in local mechanical properties, the global strength of the welds does not vary significantly. This behaviour is explained based on local plastic strain distribution analysis.