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The aim of this article is the investigation of the effects of tool tilt angle on the friction stir welding of aluminium to the steel butt joint. For this purpose, 1°, 2° and 3° tilt angles are selected to friction stir welding of AA1100 to A441 AISI, while the other process parameters (i.e. tool rotational speed, travelling speed, tool offset and plunge depth) kept constant. The results showed that with increasing tool tilt angle, the interaction between two metals and axial force increased. The increasing tool tilt angle caused more surfaces to mingle, internal mixing and frictional heat generation. The results of the microstructure of joints revealed that the AA1100 microstructure is more thermo-mechanically affected than A441 AISI. The AA1100 average grain sizes at stir zone were 1.2, 1.6 and 2 µm and at A441 AISI were 6, 7 and 9 µm at 1°, 2° and 3° tilt angles, respectively. The maximum tensile strength of joints was 75% of the aluminium base metal, which was produced at 2° tilt angle. The higher heat generation and axial force at upper tilt angle cause separation of the steel fragments on the aluminium matrix and formation of Al-Fe intermetallic compound. These phenomena lead to increase in the micro-hardness of the joint at the upper tool tilt angle.

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A prominent benefit of friction stir welding process is to join plates with dissimilar material. In this study, an attempt is made to find effects of tool offset, plunge depth, welding traverse speed and tool rotational speed on tensile strength, microhardness and material flow in dissimilar friction stir welding of AA1100 aluminium alloy and A441 AISI steel plates. Here, one factor at a time experimental design was utilised for conducting the experiments. Results indicated the strongest joint obtained at 1.3 mm tool offset and 0.2 mm plunge depth when the tool rotational speed and linear speed were 800 rev min 21 and 63 mm min 21 respectively. The maximum tensile strength of welded joints with mentioned optimal parameters was 90% aluminium base metal. Fracture locations in tensile test at all samples were in aluminium sides. Owing to the formation of intermetallic compounds at high tool rotational speed, the microhardness of joint interface goes beyond that of A441 AISI steel.

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