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The microstructure and mechanical properties improve substantially by hot working. This aspect in as-cast Mg-7.7Al-0.4Zn (AZ80) alloy is investigated by compression tests over temperature range of 30-439A degrees C and at strain rates of 5 x 10(-2), 10(-2), 5 x 10(-4) and 10(-4) s(-1). The stress exponent (n) and activation energy (Q) were evaluated and analyzed for high-temperature deformation along with the microstructures. Upon deformation to a true strain of 0.80, which corresponds to the pseudo-steady-state condition, n and Q were found to be 5 and 151 kJ/mol, respectively. This suggests the dislocation climb-controlled mechanism for deformation. Prior to attaining the pseudo-steady-state condition, the stress-strain curves of AZ80 Mg alloy exhibit flow hardening followed by flow softening depending on the test temperature and strain rate. The microstructures obtained upon deformation revealed dissolution of Mg17Al12 particles with concurrent grain growth of alpha-matrix. The parameters like strain rate sensitivity and activation energy were analyzed for describing the microstructure evolution also as a function of strain rate and temperature. This exhibited similar trend as seen for deformation per se. Thus, the mechanisms for deformation and microstructure evolution are suggested to be interdependent.

Ti + Nb-stabilised interstitial-free steel is deformed by equal-channel angular pressing (ECAP) adopting a route BC up to an equivalent strain of 24. Upon ECAP the grain size decreases to ultrafine level and it becomes strongly textured. At evm = 0.6-6, components of both {110} fiber, $$ J_{\uptheta } $$ , $$ \bar{J}_{\uptheta } $$ and of 〈111〉 fiber, D 1θ, D 2θ with common components of E θ, $$ \bar{E}_{\uptheta } $$ are existing but after evm ≥9, only 〈111〉 fiber components are observed. At large strain, evm = 9-24, 〈111〉 fiber texture is recorded with monoclinic symmetry. At evm = 0.6, coarse grains get split into deformation bands. Fragmentation of bands (at evm = 3) suppress $$ \bar{J}_{\uptheta } , $$ $$ J_{\uptheta } $$ components. At evm = 6, formation of lamellar structures increases intensity of mainly D 1θ, D 2θ. At evm = 9, oriented ribbon grains result in strong D 1θ, D 2θ components with 〈111〉 fiber. At evm = 15-24, conversion of ribbon grains to near-equiaxed shaped grains maintains 〈111〉 fiber texture with enhanced intensity of D 1θ and D 2θ components.

Microstructural evolution and related dynamic recrystallization phenomena were investigated in overlapping multipass friction stir processing (FSP) of hypereutectic Al-30 pct Si alloy. FSP resulted in the elimination of porosities along with the refinement of primary silicon particles and alpha aluminum grains. These alpha aluminum grains predominantly exhibit high angle boundaries with various degrees of recovered substructure and dislocation densities. The substructure and grain formation during FSP take place primarily by annihilation and reorganization of dislocations in the grain interior and at low angle grain boundary. During multipass overlap FSP, small second phase particles were observed to form, which are accountable for pinning the grain boundaries and thus restricting their growth. During the multipass overlap FSP, the microstructure undergoes continuous dynamic recrystallization by formation of the subgrain boundary and subgrain growth to the grain structure comprising of mostly high angle grain boundaries.