Equal Channel Angular Pressing of tin based eutectic Sn-Cu,-Mg,-Zn alloys and their thermal stability

Abstract

A 120° angled Equal Channel Angular Pressing (ECAP) die with its route B_c was used to deform pure tin and three of its eutectic alloys (Sn-0.7Cu, Sn-2.13Mg, and Sn-8.8Zn) up to eight passes at room temperature. The objective was to produce nano to ultrafine grains in these alloys for their structural and functional applications. The results show the duality of eutectic phases and intermetallic compounds: in one aspect, their fragmentation creates obstacles that hinder the growth of β-tin grain matrix during the deformation. In another aspect, they promote dynamic recrystallization during deformation and facilitate nucleation sites for the static recrystallization as well as during post-heat treatment. Quantitative analysis of the deformed microstructure presents that at least 64% of the surface fraction is consists of dynamically recrystallized (DRX) globular grains, with maximum overall dislocations densities of $~1.2\times {10}^{+14}$$~1.2\times {10}^{+14}$ after eight ECAP passes. It is an atypical observation to have an overall 10 to 16% reduction only in DRX grains and such dislocations densities after eight pass ECAP deformation from the initial state, especially compared to other medium-to-hard and higher melting temperature materials. The formed Mg₂Sn in the Sn-Mg alloy is an excellent grain and crystallite size refiner, and strengthener of the β-tin matrix compared to the intermetallic compounds of other two alloys. The sele_cted route B_c was unable to weaken the tendency for a strong deformation texture formation in pure tin and its eutectic alloys. However, it is effective in declustering and redistributing eutectics and intermetallic compounds (IMCs). Deformation texture analysis identified the evolved texture components and their locations in Euler space for the pure tin and its eutectic alloys examined in a 120° angled ECAP die. A thermal stability study justifies the role of eutectics and IMCs in tailoring the overall morphology and average size of β-tin matrix grains in the microstructure.