Enhancement of wear and ballistic resistance of armour grade AA7075 aluminium alloy using friction stir processing

Abstract

Industrial applications of aluminium and its alloys are restricted because of their poor tribological properties. Thermal spraying, laser surfacing, electron beam welding are the most widely used techniques to alter the surface morphology of base metal. Preliminary studies reveal that the coating and layering of aluminium alloys with ceramic particles enhance the ballistic resistance. Furthermore, among aluminium alloys, 7075 aluminium alloy exhibits high strength which can be compared to that of steels and has profound applications in the designing of lightweight fortification structures and integrated protection systems. Having limitations such as poor bond integrity, formation of detrimental phases and interfacial reaction between reinforcement and substrate using fusion route to deposit hard particles paves the way to adopt friction stir processing for fabricating surface composites using different sizes of boron carbide particles as reinforcement on armour grade 7075 aluminium alloy as matrix in the present investigation. Wear and ballistic tests were carried out to assess the performance of friction stir processed AA7075 alloy. Significant improvement in wear resistance of friction stir processed surface composites is attributed to the change in wear mechanism from abrasion to adhesion. It has also been observed that the surface metal matrix composites have shown better ballistic resistance compared to the substrate AA7075 alloy. Addition of solid lubricant MoS 2 has reduced the depth of penetration of the projectile to half that of base metal AA7075 alloy. For the first time, the friction stir processing technique was successfully used to improve the wear and ballistic resistances of armour grade high strength AA7075 alloy.

Friction stir welding of AA5052: the effects of SiC nano-particles addition

“…The wear resistance of different materials and composites processed by the FSW and FSP has been studied by many researchers [21][22][23][24]. The metal matrix composites prepared in these works exhibited lower friction coefficient and better wear resistance compared to unprocessed specimens.…”

Cast aluminium matrix composites modified with using FSP process – Changing of the structure and mechanical properties

“…Grains are observed to reduce their boundaries, silicon eutectic is refined, and so are the intermetallic phases of the α-FeAlSi type and other [20,30], all of them being combined with the processes of structure renewal (recovery, recrystallisation) and supersaturation [20,[25][26][27][28][29]. Previous works usually discussed the problem of microstructure homogenisation ignoring subtle differences in the distribution of different phases, which can be very important from the point of view of changes in the mechanical [16,33,67], as well as tribological properties [33,67,68]. The most important, however, is all the time the assessment of an impact that changes in the composite structure due to the effect of hardening may have on the mechanical properties in individual areas of the modified composite.…”

The Effect of Aging Treatment on the Friction-Stirprocessed Aa7075 Alloy With and Without Surface Nano-Dispersion

“…FSP has many advantages compared to other surface modification techniques based on liquid and fusion processes, since the latter cannot avoid interfacial reactions between the metal matrix and reinforcement used. Such interactions may lead to defects including pin holes, segregation, shrinkage cavity, grain coursing and pores [4,5]. Mishra [1] has explained the main advantages of using FSP as a surface modification technique to be: 1) the FSP is carried out in solid state, so, interfacial reaction and formation of detrimental phases are avoided, 2) the FSP results in significant grain refinement in the surface layer, since the wrought microstructure is desirable for enhanced fracture properties as compared with the solidified microstructure that results from laser processing or high-energy electron beam irradiation.…”

“…The process has been also applied to the manufacture of surface composites by incorporating nano-sized alumina into AA6082 aluminium alloy and for the uniform distribution of SiC particles into a surface layer of A1050-H24 alloy [5,6]. The new surfaces showed defect free interfaces and the perfect bonding between the substrate and the surface composite.…”

“…Though steel is the strongest competitor in military applications due to its high strength, hardness, energy absorbing properties, and greater notch toughness, aluminum is still the future element for those applications where enhanced mobility with safety are the main requirements [8][9][10]. However Backman et al and Corbett et al have shown that aluminium alloys have special properties that can limit their usage as armor material specifically: lower young's modulus, lower sensitivity to strain rate, and lower melting point [5,[11][12].…”