No abstract

No abstract

No abstract

In this study, a new solid-state technique of friction stir additive manufacturing (FSAM) based on friction stir welding (FSW) principle was used to build successfully a multilayered stack of an Al-based component. The results show that a hook stretches into the nugget zone on advancing side, while it moves upwards to the periphery on retreating side for a single-level welding. With manufacturing the second layer, the hooks bend outward significantly attributing to the extrusion of above plastic material, which can avoid the hook to stretch into the stirred zone. A transition zone (TZ) is also formed near the interface between two layers. In addition, fine equiaxed grains are observed due to the dynamic recrystallization in the whole. However, a difference in grain size still exists through the build direction and in the TZ is forming coarse band grains. A similar change occurs in the precipitate morphology, size, and distribution. Form the top to the bottom, the microhardness changes dramatically, and a maximum 115 HV at the top is obtained. The tensile strength of all the slices increases and the elongation decreases slightly in comparison of Al substrate, and the slice top has the highest mechanical properties, which is attributed to fine grains and desirable precipitate characterization.

Two-millimeter-thick 2060 Al-Li alloy plates were friction stir welded under a welding speed of 95-150 mm/min and rotation speed of 750-1500 rpm. The effects of welding speed and rotation speed on formation quality, microstructure, secondary phase particles' transformation, and mechanical properties of the joints were investigated. The results show that defect-free joints are produced for varying friction stir welding (FSW) parameters, and nugget size increases firstly and then decreases with increasing rotation speed or decreasing welding speed. The weld nugget zones (WNZs) have fine dynamically recrystallized grains, and the size decreases to 7.9 μm with increasing rotation speed to 1180 rpm or decreasing welding speed to 118 mm/min, while the grains are coarsened at 1500 rpm or 95 mm/min. A similar trend occurs in the transformation of secondary phase particles, whose size is the smallest in WNZ at 1180 rpm-118 mm/min. All joints exhibit softened zones where the hardness is the lowest, and the joints fracture from WNZs or heat-affected zones. The joints welded at 1180 rpm-118 mm/min perform the highest ultimate tensile strength of 495 MPa, yield strength of 380 MPa, and elongation of 10.2 %. With increasing rotation speed or decreasing welding speed, the strengths and elongation of the joints increase firstly and then decrease.