The effect of pin profiles on the microstructure and mechanical properties of underwater friction stir welded AA2519-T87 aluminium alloy

Abstract

Background: AA2519-T87 is a new armour grade aluminium alloy employed in the fabrication of light combat military vehicles. Joining of this material using fusion welding processes, results in the formation of solidification defects like porosity, alloy segregation and hot cracking. In order to overcome the solidification related problems, solid state welding processes such as friction stir welding (FSW) can be used. Though the joining takes place below the melting temperature of the material, the thermal cycle experienced by the thermo-mechanical-affected zone (TMAZ) and heat-affected zone (HAZ) is causing grain coarsening and precipitates dissolution in the age-hardenable aluminium alloys, which deteriorate the joint properties. To get rid of this problem, underwater friction stir welding (UWFSW) process can be employed. The water cooling reduces the heat, and thus, the thermal softening required taking place in TMAZ and HAZ. Therefore, the material flow is entirely different in FSW and UWFSW.

Influences of tool traverse speed on tensile properties of air cooled and water cooled friction stir welded AA2519-T87 aluminium alloy joints

“…The joint configuration of 150 mm × 150 mm × 6 mm was used in the investigation. Form the previous investigation, the present authors found that the taper threaded tool was well suited for joining this material and thus it was used in this investigation (Sree et al, 2015b). The tool traverse speed was varied from 20 mm/min to 40 mm/min by keeping other parameters constant.…”

Effects of Rapid Cooling on Properties of Aluminum-Steel Friction Stir Welded Joint

“…Forasmuch as the CO 2 cooling media causes higher cooling rate among other conditions, complete material flow is suppressed especially at the weld root and causes weak mechanical bonding. Additionally, excess cooling rate seems to lead to high contraction and separation of base metals [ 46 ]. The lower stirring action and weaker mechanical interlocking at lower area of stir zone are the main hypothesis for this material behavior.…”

“…In the case of WF-FSW, the water is liquid until 100 • C and absorbs heat with specific heat capacity that is smaller than the latent heat of evaporation of CO 2 , thus the cooling rate and cooling capacity of CO 2 is larger than water [45]. With AF-FSW, the specific heat capacity of the air is smaller than the specific heat capacity of water; consequently, the cooling rate and cooling capacity of water is larger than those of compressed air [46]. The recorded temperature by NT3 in both aluminum and steel side proved that the generated heat diffuses into the leading edge (LE) of the tool.…”

Investigation of Mechanical and Microstructural Properties of Welded Specimens of AA6061-T6 Alloy with Friction Stir Welding and Parallel-Friction Stir Welding Methods

“…According to Figure 7, in the AP-FSW and RP-FSW processes, the welding area in the welded specimens increased with increasing the tool offset in the first and second passes. In the FSW process, the SZ is generally formed at the tool pin passage locus, and its width is approximately equal to the diameter of the tool pin [8,37,47,63,64]. In P-FSW techniques, in addition to the dimensions of the tool, the width of this area depends on the tool offset in the first and second welding passes.…”