A B S T R A C TThe effect of processing parameters on static strength and fracture mechanisms of dissimilar friction stir spot welds between different aluminium alloys was studied. Tensile shear strength increased with decreasing tool rotational speed and increasing tool holding time, while cross tension strength decreased with increasing both parameters. Two fracture modes were observed: nugget shear fracture and mixed mode fracture under tensile shear loading, and debonding and pull-out of the nugget under cross tension loading. Based on experimental observation, the dependence of static strength on processing parameters and the occurrence of different fracture modes were discussed.Keywords friction stir spot welding; processing parameter; static strength.
N O M E N C L A T U R E F c = cross tension force (kN)F s = tensile shear force (kN)
I N T R O D U C T I O NIn order to achieve high performance and energy saving in machines and structures, there have been increasing applications of lightweight materials such as aluminium and magnesium alloys in transportation systems, particularly in the automotive and aerospace industry. In manufacturing machines and structures, joining of components is necessary, thus joining techniques such as welding, rivet and clinching have been employed for joining sheets of these materials. Fusion welding is the most commonly used technique, but a rather new joining method, friction stir welding (FSW), has been developed and is becoming an important joining technique for lightweight materials. This method has several advantages over the traditional fusion welding techniques, such as; solid-state process, ease of handling, joining of dissimilar materials and materials that are difficult to fusion weld, low distortion, excellent mechanical properties and little waste or pollution.Recently, a new spot welding using FSW has been developed, friction stir spot welding (FSSW) or friction spot joining (FSJ) 1,2 . This technique is expected to used in the automotive industry for joining body parts made of aluminium sheet, as it has the same advantages as FSW. In adCorrespondence: Y. Uematsu. dition resistance spot welding, widely used at present, has disadvantages such as high operating and investment cost and poor weld strength. For future applications of FSSW of critical components, it is important to evaluate the weld strength and fracture mechanisms. In FSSW, many processing parameters influence the weld properties, such as; tool rotational speed, tool holding time, downward force and tool geometry exist, but there have been very limited studies on the effect of individual parameters on the mechanical properties. [2][3][4][5][6] In the present study, tensile shear tests and cross tension tests were performed using lap-shear specimens and crosstension specimens, respectively, of dissimilar friction stir spot welds between 2017-T6 and 5052 aluminium alloys. The effect of processing parameters such as tool rotational speed and tool holding time on static strength was evaluated and the fract...
