Local strength of friction stir (FS) welds and FS processed aluminium alloys in heat treatable aluminium alloys is dominated by precipitation hardening. Strengthening due to stored dislocations is generally limited to 40MPa, and grain size strengthening is generally less than 10MPa. Local crystallographic texture can cause yield strength variation on the order of 5%. Published models for strengthening of FS welds make a range of simplifying assumption which can cause uncertainties in the predictions of up to 50MPa. Possible improvements are explored.
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