Tool rotational speed impact on temperature variations, mechanical properties and microstructure of friction stir welding of dissimilar high-strength aluminium alloys

Abstract

Temperature variations during friction stir welding result from the heat generated by the frictional action of a rotating tool on the workpiece. This temperature distribution affects the mechanical behaviour and ultimately the quality of welds produced. The study of the correlations between process parameter, temperature, mechanical properties and microstructure has become imperative in order to promote welds devoid of defects and possessing sound mechanical properties and to establish a temperature feedback control for effective components designs for industrial applications. This work studied the impact of tool rotational speed on temperature profile, mechanical behaviour and microstructure of friction stir welding of dissimilar aluminium alloy 6101-T6 and 7075-T651. Processing parameters of three different rotational speeds with values 1250 rpm, 1550 rpm and 1850 rpm and a constant travel speed of 50 mm/min were employed. The temperature profile was measured with one end of thermocouple wires embedded in the plates and the other end connected to a data capturing software device. The temperature profile indicates that the temperature rises with time and is higher at the retreating sides than at the advancing side of the weld. The tensile test results show that the ultimate tensile strength decreases as the temperature increases. Microstructural observations of weld zone revealed non-uniformity in material flow. However, more material penetration into each other occurred more at 1550 rpm.

Microstructure and mechanical properties of dissimilar friction stir welds of AA2014 and AA7075

“…A similar result was reported for dissimilar welds of AA2219 and AA7475 and AA6061-T6 and AA7075-T651 alloys, welds fractured from advancing side HAZ of low strength AA2219 AA6061-T6, respectively. 30,31 The fracture location from the weld centerline exhibited a trend similar to UTS with a change in WS or RS. With an increase in WS, fracture location moved toward the weld center at constant RS.…”

“…33 The growth and coalescence of voids govern the fracture behaviors as local plastic instability forms microscopic flaws upon the growth of voids to critical sizes. 31 Fragmented precipitate could be seen inside the dimples with well-defined tear ridges. The morphology of these precipitates was found to vary with processing parameters.…”

Impact of tool profile on mechanical behavior and material flow in friction stir welding of dissimilar aluminum alloys

“…The friction between the workpiece and the rotating tool shoulder produce heat. This heat softens the materials at the workpiece joint interface causing the rotating pin to penetrate, stir and mixes the plasticized materials to produce bonding . This technology has become a very suitable method for joining aluminum alloys .…”

Review of Friction Stir Processing (FSP) Parameters and Materials for Surface Composites

“…Material stirring begins with rotating action of the tool, proceeds with both rotational and translational, and finishes with pure rotational movement of the tool which doesn't end as long as tool and specimen are in contact [5]. It is proven that with increase of the rotational speed, the generated temperature increases significantly [28][29][30]. When rotational speed is of some constant value, the average welding temperature is increased when translational speed is decreased [31].…”