Study on weldability of similar aluminium alloys by friction spot welding

Abstract

The objective of the present work is to access the weldability of a similar configuration of AA5454-H22 by Friction Spot Welding, test the strength of the weld in different configurations and analyse the parameters that contribute to the behaviour of the joint under different types of loading. The welds were produced in Lap-Shear and Cross-Tensile configuration for static loading experiments and Fatigue samples were also produced to characterize the performance under cyclic loading. Regarding the structural changes introduced by the process, the microstructure was thoroughly examined, the hardness and grain size of each zone were measured and finally the fracture surfaces were observed. The thermal cycle was studied to quantify the variation of temperature with time in the plates. The weldability study and the use of a Box-Behnken Design of Experiments led to an optimum parameter and the statistical analysis allowed the conclusion that Plunge Depth is the most prominent parameter in the process for this particular material. The most effective welds of the initial range are, generally, the combinations with slower Feeding Rate, higher Rotational Speed and a Plunging Depth of about 20% in the lower plate. Those combinations translate into a high heat input. Defects such as hook, inadequate bonding and insufficient refill were found in different parameters. The morphology of the hook such as the Bending Angle and the Hook Height proved to have a definite effect on the strength of the welds and on the fracture mode, respectively. According to the data gathered in fracture analysis, the bonding of the plates is stronger in the area directly affected by the sleeve and then gradually decreases towards the centre of the weld, where the bonding is considerably weaker.