TWO-DIMENSIONAL MAPPING OF RESIDUAL STRAINS IN 6061-T6 ALUMINUM ALLOY FRICTION STIR WELDS

摘要

The residual strain profiles were measured through the thickness of friction-stir welded (FSW)rnplates using neutron diffraction to study the relationship between the angular distortion and thernresidual strain distribution. Three different weld specimens were prepared from a 6061-T6rnaluminum alloy with the purpose of separating the effects of the frictional heat and plasticrndeformation on the residual strain distribution and the angular distortion in the weld plate: (Casern1) a plate processed with both stirring pin and tool shoulder, i.e., a regular FSW subjected to bothrnplastic deformation and frictional heat, (Case 2) a plate processed only with the tool shoulder,rni.e., subjected mainly to the frictional heating, and (Case 3) a plate processed only with the pin,rni.e., subjected mainly to the plastic deformation. Case 1 showed little bending of the weld platernabout longitudinal (welding) direction, Case 2 exhibited a concave bending, and the Case 3rnexhibited a convex bending, suggesting that different residual strain profiles exist through thernthickness of the plates. Three principal strain components were measured across the weld line atrnthe face, center, and root of the cross section of the welds. Case 1 showed little variations in thernresidual strain profiles though the thickness while Case 2 showed significant variations.rnUnfortunately, results from Case 3 were questionable due to the presence of a groove on thernsurface of the plate and, hence, it may not truly represent the “pin-only” case. The comparisonrnbetween Case 1 and Case 2 suggests that an optimal combination of the pin action (plasticrndeformation and heat transfer through the thickness of the plate) and the shoulder actionrn(heating) could minimize (or provide intentional manipulation of) the through-thickness variationrnof residual strains and angular distortion in the FSW plates.