Abstract
This study focuses on the properties and process parameters dictating behavioural aspects of friction stir welded Aluminium Alloy AA6061 metal matrix composites reinforced with varying percentages of SiC and B4C. The joint properties in terms of mechanical strength, microstructural integrity and quality were examined. The weld reveals grain refinement and uniform distribution of reinforced particles in the joint region leading to improved strength compared to other joints of varying base material compositions. The tensile properties of the friction stir welded Al-MMCs improved after reinforcement with SiC and B4C. The maximum ultimate tensile stress was around 172.8 ± 1.9 MPa for composite with 10% SiC and 3% B4C reinforcement. The percentage elongation decreased as the percentage of SiC decreases and B4C increases. The hardness of the Al-MMCs improved considerably by adding reinforcement and subsequent thermal action during the FSW process, indicating an optimal increase as it eliminates brittleness. It was seen that higher SiC content contributes to higher strength, improved wear properties and hardness. The wear rate was as high as 12 ± 0.9 g/s for 10% SiC reinforcement and 30 N load. The wear rate reduced for lower values of load and increased with B4C reinforcement. The microstructural examination at the joints reveals the flow of plasticized metal from advancing to the retreating side. The formation of onion rings in the weld zone was due to the cylindrical FSW rotating tool material impression during the stirring action. Alterations in chemical properties are negligible, thereby retaining the original characteristics of the materials post welding. No major cracks or pores were observed during the non-destructive testing process that established good quality of the weld. The results are indicated improvement in mechanical and microstructural properties of the weld.
Highlights
In many industrial applications, aluminium alloys are reinforced with hard ceramic particles to enhance the mechanical properties of aluminium metal matrix composites (Al-MMCs) [1,2,3]
To strengthen Al-MMCs, SiC (325 nm mesh size) and B4C (30 nm) particles were reinforced in the metal matrix (Figure 2)
It was observed that sample #1 had the lowest B4C content had the highest tensile strength (172 MPa) compared to the other samples (Figure 5)
Summary
Aluminium alloys are reinforced with hard ceramic particles to enhance the mechanical properties of aluminium metal matrix composites (Al-MMCs) [1,2,3]. In the friction stir welding (FSW) process, a non-consumable rotating tool having higher toughness than the base material is pitched into the faying/butt ends of the plates to be welded. Wook et al [19] achieved uniform distribution of reinforced particles in weldment due to friction of FSW tool, and SiC increases the hardness of the Al-MMCs. Limited literature reports are available on appropriate mixing percentages of SiC and B4C reinforcements on Al-MMCs for which industrially acceptable mechanical property ranges and microstructural integrities for reliability are established. Reports on weldability studies on these Al-MMC’s are sporadic, lacking an interdisciplinary treatment This provides a broader scope for exploration regarding the thermal implications of FSW on microstructures, process parametric influences on weld efficiency and mechanical behavioural analysis. The energy generated during the FSW process in terms of heat is estimated to examine the thermal behaviour of the weld in different regions of the joint, which governs the microstructural grain sizes and the consequential, mechanical properties
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