Friction Stir Welding of Dissimilar Al/Al and Al/Non-Al Alloys: A Review
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INTRODUCTION
MANY components produced for modern industrial applications require the optimization of multiple thermal and mechanical properties, making the selection of a single ideal build material increasingly difficult. Joining dissimilar materials allows for the utilization of the best properties of both materials. Steel, owing to its high strength, high toughness, and low cost, serves as one of the most popular structural materials in many industries. Wrought Al alloys are widely used in transportation industries due to their high strength and lightweight characteristics. In order to reduce the weight and improve the fuel efficiency of aircraft and automobiles, Al alloys have been introduced in the fabrication of aircraft and automobile structures. Honda, for example, produced an Al-steel automobile subframe in 2012, which reduced the total body weight and electricity consumption of the vehicle by 25 and 50 pct, respectively. The demand for lightweight and low energy consumption vehicles gives rise to the application of joining Al alloys with Mg alloys due to their high specific strength relative to traditional supporting materials. The combination of lightweight Al alloys with the high thermal and electrical conductivity offered by Cu has significant potential in electronic applications and in the power generation industry as well.
XIANGBIN WANG, YI PAN, and DIANA A. LADOS are with the Worcester Polytechnic Institute, Integrative Materials Design Center, Worcester, MA 01609. Contact e-mail: [email protected] Manuscript submitted November 4, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Friction stir welding (FSW), illustrated in Figure 1,[1] was developed by The Welding Institute (TWI), and is a solid-state joining technique that provides many advantages relative to conventional welding processes. A non-consumable rotating tool with a shoulder-pin structure is plunged into the abutting edge of plates and moves along the interface (the weld line). The advancing side of the weld, denoted throughout this paper as AS, is the side where the tangential velocity of the rotating tool corresponds to the tool’s traverse direction, while on the retreating side, RS, they are in opposite directions. During FSW, the heat generated by the friction between the welding tool and workpiece softens the materials. With the combination of the stirring and traverse actions of the tool, material is transported from the front to the back of the tool to produce the joint. FSW is conducted at a temperature below the melting points of the base materials so the low heat input of FSW gives rise to some unique properties in the resulting welds. No solidification cracking occurs in FSW, and desirable levels of the base metal strength can be retained. The low heat generation also suppresses the formation of brittle intermetallic compounds, which enhances the fatigue resistance of the materials. The low heat input also leads to reduced amounts of residual stress and distortion compared to traditional welding. FSW has been widely adopted in ind
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