Effects of tool shoulder geometry on mechanical properties and microstructure of friction-stir welded joints of AA5083-0 aluminium alloys

Abstract

Shoulder geometry is an important geometrical feature of tool design in friction stir welding since it has a strong effect on heat generation and material flow. Inthis paper the effect of shoulder geometry of tool on mechanical properties, microstructure evolution, and thermal history of friction stir welded joints of AA5083-O aluminium alloy. Two different shoulder geometries of tool named concave and featured (concentric circles) were used, both with cylindrical threaded pin. A set of samples were fabricated using a milling machine and a factorial experimental design to estimate the effects of process parameters (rotational and welding speed) and shoulder geometry on welded joints. Tensile strength, hardness, and microstructure evolution were experimentally measured. These observations were complemented with results obtained from a finite element modelling to calculate thermal history in welded joints. The results showed that the combination of revolution pitch R-value and shoulder geometry of tool were the most significant factors, affecting to mechanical properties, thermal behaviour, and microstructure evolution. The best tensile properties were obtained with a featured shoulder tool using 1400 rpm and 16 mm.min-1, and 1085 rpm and 11 mm.min-1for rotational and welding speed. The same parameter combination resulted in a joint efficiency of 70% and 65%, respectively. In addition, the results of evaluation using an ANOVA analysis with fixed factors showed that increasing R-values produces statistically significant differences in ultimate strength (Sut) values.

Keywords

• friction stir welding
• aa5083 aluminium alloys
• thermal distribution
• microstructure
• process parameters