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In this paper, we report the formation of an atypical double twinning sequence in Zircaloy-4 during rolling at room temperature. The grain orientation analysis based on electron backscattering diffraction (EBSD) data reveals that this double twinning mode is of the 11 2 ̅ 1 - 10 1 ̅ 2 type, namely, the secondary 10 1 ̅ 2 twin generated within the primary 11 2 ̅ 1 twin. Based on the combinative analysis of Schmid factor and local strain accommodation, the formation and variant selection mechanism of this double twinning are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Composite aluminium alloys reinforced with Al2O3p particles have been produced by squeeze casting followed by hot extrusion and a precipitation hardening treatment. Good mechanical properties can be achieved, and in this paper we describe an optimization of the key processing parameters. The parameters investigated are the extrusion temperature, the extrusion rate and the extrusion ratio. The materials chosen are AA 2024 and AA 6061, each reinforced with 30vol.% Al2O3 particles of diameter typically in the range from 0.15 to 0.3μm. The extruded composites have been evaluated based on an investigation of their mechanical properties and microstructure, as well as on the surface quality of the extruded samples. The evaluation shows that material with good strength, though with limited ductility, can be reliably obtained using a production route of squeeze casting, followed by hot extrusion and a precipitation hardening treatment. For the extrusion step optimized processing parameters have been determined as: (i) extrusion temperature=500°C–560°C; (ii) extrusion rate=5mm/s; (iii) extrusion ratio=10:1. [Copyright &y& Elsevier]