Abstract
Al/Mg dissimilar welds were successfully fabricated by refill friction stir spot welding using a grooved sleeve tool. Influences of sleeve penetration depth and rotational speed on the weld formation and mechanical performance were systematically evaluated in terms of welding parameter optimization, interfacial bonding mechanism, hardness distribution and welded joint strength. The results indicated that the success of joining Al alloy to Mg alloy significantly depends on tool sleeve penetration depth. The interfacial bonding mechanism compromised both metallurgical bonding and mechanical inter-locking. Intermetallic compound layers of Al3Mg2 and Al12Mg17 were formed at the Al/Mg interface. The thickness of the intermetallic compound (IMC) layer at the weld center increased from 20–30 μm to 40 μm when the rotational speed increased from 1000 to 2000 rpm. The minimum hardness was 80 HV in Al 7075 and 52 HV in ZEK 100; both were measured in the heat affected zone. The welded joint lap shear strength decreased, and the scatter increased with the increasing of rotation speed, whose maximum was 3.6 kN when the rotational speed was 1000 rpm. In addition, the failure mechanism was determined by tool rotational speed, and found to be interfacial failure under a rotational speed of 1000 rpm and nugget pullout under a rotational speed of 2000 rpm.
Highlights
With the purpose of reducing structural weight and providing environmental protection, lightweight materials such as Al and Mg alloys have been used to replace conventional steel structures in the automotive, aerospace, high speed rail, and shipbuilding industries [1]
Several approaches have been adopted to join Al/Mg dissimilar welds, including: (i) mechanical joining technology such as self-pierce riveting [3]; (ii) fusion welding such as laser welding [4,5,6], cold metal transfer welding [7], TIG welding [8], and resistance spot welding [9]; and (iii) solid-state joining technology such as ultrasonic spot welding [10,11,12], friction stir welding (FSW) [13,14,15,16], and conventional friction stir spot welding (FSSW) [16,17]
The base materials chosen for this study were 0.9 mm thick Al 7075-T6 and 1.5 mm thick ZEK100-O Mg alloy, and were provided by Ford Motor Co and Magnesium Elektron, respectively
Summary
With the purpose of reducing structural weight and providing environmental protection, lightweight materials such as Al and Mg alloys have been used to replace conventional steel structures in the automotive, aerospace, high speed rail, and shipbuilding industries [1]. It should be noted that i necessary to form an IMC layer to promote metallurgical bonding at the Al/Mg interfa Compared to these joining methods, solid-state welding technologies have significant vantages because they suppress temperature rise and can avoid bulk. As a which results in stress concentration and significantly decreases the weld strength [20 solid-state joining technology, conventional FSSW has the same merits as FSW [19]. Found that a grooved sleeve can significantly increase plastic deformation, and crea microstructure, such as crystal defects and grain boundaries [42] It is of interest a mechanical inter-locking joining mechanism in Al. 7075 similar and Al to apply the grooved sleeve tool to joining the Al/Mg dissimilar weld. Crystals 2021, 11, 429 article discusses the interfacial bonding and mechanical performance of Al/Mg dissimilar welds using a grooved sleeve
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