Influence of Weld Defects and Postweld Heat Treatment of Gas Tungsten Arc Welded AA 6061 T651 Aluminum Alloy

Abstract

Welding defects and the reduction of mechanical performances are the foremost problems for fusion welded aluminum alloys joints. The influences of weld defects and postweld heat treatment (PWHT) on tensile properties of gas tungsten arc (GTA) welded aluminum alloy AA6061T651 joints are investigated in this current study. All welded specimens are nondestructively inspected with phased array ultrasonic testing (PAUT) to classify weld defect and measure the projected defects arearatio (AR). Ultimate tensile strength (UTS) decreased linearly with the increase of the size of weld defect but tensile toughness behaved nonlinearly with defect size. Depending on defect size, defective samples' joint efficiency (JE) varied from 35% to 48% of base metal's (BM) UTS. Defectfree aswelded (AW) specimens observed to have 53% and 34% JE based on UTS and yield strength (YS) of BM, respectively. PWHT was applied on defectfree welded specimens to improve tensile properties by precipitation hardening, microstructures refining, and removal of postweld residual stresses. Solution treatment (ST) (at 540 آ°C) followed by varying levels of artificial agehardening (AH) time was investigated to obtain optimum tensile properties. For GTAwelded AA6061T651, peak aging time was 5 hr at 180 آ°C. PWHT specimens showed 85% JE based on UTS and up to a 71% JE based on YS of BM. However, toughness values decreased about 29% due to the presence of precipitatefree fusion zones. The experimental investigations can be used to establish weld acceptance/rejection criteria and for the design of welded aluminum alloy structures.