Developing superplasticity in a magnesium alloy through a combination of extrusion and ECAP

• Published in: Acta materialia 2003-06, Vol.51 (11), p.3073-3084
• Main Authors: Matsubara, K., Miyahara, Y., Horita, Z., Langdon, T.G.
• Format: Article
• Language: English
• Subjects: Applied sciences; Cross-disciplinary physics: materials science; rheology; Equal-channel angular pressing; Exact sciences and technology; Extrusion; Magnesium; Materials science; Metals. Metallurgy; Other heat and thermomechanical treatments; Physics; Superplasticity; Treatment of materials and its effects on microstructure and properties; Ultrafine-grained microstructure
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/S1359-6454(03)00118-6

A new processing procedure was applied to a cast Mg-9% Al alloy. This procedure involves the sequential application of extrusion and equal-channel angular pressing and is designated EX-ECAP. Experiments show that the Mg-9% Al alloy has an initial grain size of ~50 μm after casting but this is reduced to ~12 μm after extrusion and it is further reduced to ~0.7 μm when the extruded alloy is subjected to ECAP for 2 passes at 473 K. Although the cast alloy exhibits extremely limited ductility and the extruded alloy is only moderately ductile, it is demonstrated that processing by EX-ECAP produces excellent superplastic ductilities including the occurrence of both low temperature superplasticity and high strain rate superplasticity. The EX-ECAP process is less effective when the ECAP step is conducted at 573 K because, although the pressing is then very easy, there is significant grain growth at this higher temperature.