Mechanical properties of cryogenically treated AA5083 friction stir welds

In this investigation, the effect of cryogenic treatment (CT) on room temperature mechanical properties was investigated. 10 mm thick AA5083-H321 plates were friction stir welded and the welds were deep treated cryogenically using liquid nitrogen. The effect of CT on the mechanical properties of the welds was investigated by hardness, tensile, and impact tests. Weld microstructures were also examined by light microscopy and scanning electron microscopy. The cryogenic treatment was found to marginally improve the hardness across the weld. The CT was found to exhibit a minimal improvement in both yield and tensile strengths of the base material and the welded joint. However, the percentage elongation was not affected by the CT process. Tensile failures occurred in the weld nugget and thermo-mechanically-affected zone interface for both untreated and treated welds. The impact toughness was found to decrease after the CT, and the effect is more pronounced in the welds than in the base material. The effect of CT on microstructures was not found to be noticeable. On the whole, it is understood that there is a slight increase in strength and hardness and a slight decrease in toughness as a result of cryogenic treatment.