Plastic behavior-dependent weldability of heat-treatable aluminum alloys in friction stir welding

Abstract

The quality of friction stir welding joints is intimately related to the correct mixing of the stirred material. The material flow is strongly dependent on the plastic behavior of the welded alloy. For this reason, the friction stir weldability depends on the structure, microstructure and chemical composition of the base material. In this work, in-plane forces and acoustic emission signals were monitored while welding two heat-treatable aluminum alloys. The forces evolutions suggested possible continuous and intermittent material flow during friction stir welding depending on the welding parameters. The differences observed in the in-plane forces were corroborated by acoustic emission, confirming the modification in the material flow phenomenology. Therefore, differences observed in aluminum alloys' friction stir weldability are due to the plastic behavior at high temperature and medium-high strain rate. The higher the deformability of the aluminum alloys, the wider the weldability window in friction stir welding because of continuous material flow in an extended range of process parameters.

Effect of Process Parameters on Friction Stir Welded Joints between Dissimilar Aluminum Alloys: A Review

“…The extent of these changes depends on factors such as the alloy composition, welding parameters, and cooling rate. Differences in microstructure, such as grain size, phase distribution, and precipitate formation, between the heat-treatable and non-heat-treatable alloys can affect the joint's mechanical properties, including strength, hardness, and corrosion resistance [37,46,47]. In heat-treatable aluminum alloys, the process of softening is linked to the dissolution of strengthening precipitates and the growth of grain size when subjected to welding-induced thermal cycles.…”

A semi-empirical model for peak temperature estimation in friction stir welding of aluminium alloys

“…Several bead-on-plate runs 140 mm long along the rolling direction were made on 3-mm thick aluminium alloys. They were chosen for their great application in friction stir welded structures in various industrial sectors [3]. Moreover, the interest derives from their different thermal characteristics and alloys type (heat treatable and strain hardened).…”

“…The final quality of the process, i.e. defective or sound joint, is strongly influenced by the temperatures reached in the hot zone around the tool [3]. Also, the final microstructure in the various areas that make up the joint and the consequent mechanical properties [4], as well as any residual stress [5] that may be found in the welded plates, are other components driven by the thermal history of the material, understood as the maximum temperatures reached and the severity of the thermal cycles (time spent at certain temperatures by the base material).…”

Studies on the Quality of Joints and Phenomena Therein for Welded Automotive Components Made of Aluminum Alloy—A Review

“…FSW causes various microstructural changes in both the HAZ and the weld zone, depending on the alloy set, process parameters, and the cooling rate. Differences in grain size, phase distribution, and precipitate formation between heat-treatable and non-heat-treatable alloys influence the joint's strength, hardness, and corrosion resistance [258,267,268]. In heat-treatable Al alloys, material softening is strongly affected by the dissolution of strengthening precipitates and grain size growth when subjected to process-induced thermal cycles.…”