Formation characteristic, microstructure, and mechanical performances of aluminum-based components by friction stir additive manufacturing

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.

Establishing Mathematical Models to Predict Grain Size and Hardness of the Friction Stir-Welded AA 7020 Aluminum Alloy Joints

“…They showed that the joint welded at a tool rotational speed of 1400 rpm, welding speed of 60 mm/ min, axial force of 8 kN, using the tool with 15 mm shoulder diameter, 5 mm pin diameter, and 45 HRC tool hardness resulted in better mechanical properties compared to other joints. Furthermore, Yuqing et al [15] have explored the effect of tool eccentricity on the microstructure and mechanical properties of the friction stir-welded 7075 aluminum alloy thick plate. They have revealed that the joints welded by the pin with 0.2 mm eccentricity perform the highest tensile strength and elongation, which is attributed to better interfaces, finer grains, and more dispersive secondary phase particles.…”

“…Similarly, it has been reported that higher heat input conditions can result in the secondary phase particles dissolving or becoming coarser. [15] The SEM micrographs of the SZ of the joints welded at lower and higher heat input conditions are illustrated in Figure 8. It can be seen from Figure 8 that higher heat input condition causes fewer and larger precipitates in the SZ of the joint.…”

“…By substituting Eqs. [14] into [15] and then taking the natural logarithm, the resulted formula will be as follows:…”

“…[13][14][15][16][17][18][19][20][21][22] Rajakumar et al [13] have studied the effect of FSW parameters and tool temperature on mechanical properties of the AA 7075-T6 alloy. They showed that the joint welded at a tool rotational speed of 1400 rpm, welding speed of 60 mm/ min, axial force of 8 kN, using the tool with 15 mm shoulder diameter, 5 mm pin diameter, and 45 HRC tool hardness resulted in better mechanical properties compared to other joints.…”

Friction additive manufacturing technology: A state-of-the-art survey

“…Therefore, the microstructure in each layer is different in the friction stir AM process. 59 Yuqing et al 42 carried out a ninelayer friction stir additive for 5 mm AA7075-O sheet. The material in center stirred zone was fully mixed showing no grooves and holes.…”