Papers by Keyword: Microstructural Control

Abstract: Distribution of microstructure and hardness by RBT (Rotary Bending and Tensile) loading at ambient temperature is presented. Grain size is one of the important parameters of microstructures of alloys, and affects mechanical characteristics depending on deformation conditions. At higher temperatures, coarsening of grain size improves creep strength, while the finer improve tensile strength at ambient temperature. Grain size shows opposite effect on strength of alloys depending on temperatures and not always possible to improve strength both at ambient and high temperatures. Authors have attempted microstructural control by formation of distribution of plastic strain prior to heat treatment of aluminum alloys to obtain well-balanced strength both at high and ambient temperatures. In this report, distribution of grain size and hardness in 2017 aluminum by RBT loading are presented, and compared with results in 1070 reported previously. RBT loading equipment is designed for combined loading by rotary bending and static tensile loading to distribute plastic strain. In 2017 alloy, obtained microstructure after suitable heat treatment show distribution of hardness, while grain size show homogeneous distribution. The distributions, however, are different from that in 1070 alloy.

Abstract: The Zn-22Al alloy with fine-equi-axed has been well known as a typical superplastic metallic material [1]. In the present study, The Zn-22Al alloy ingot of 20mm thickness was homogenized, either air-cooled or water-quenched, and then hot-rolled to a thickness of 2mm. Microstractural observation, showed that in the air-cooled specimens lammellar microstructure was formed after homogenization, and become fragmented to fine-grained microstructure as the hot rolling process proceeded. In the water-quenched specimens, equi-axed fine-grained microstructure with grain size under 2.1μm was attained and maintained throughout the hot rolling process.

Abstract: The Zn-Al eutectoid alloy has been well known as a typical superplastic metallic material with small grain sizes. In the present study, controlling conditions in hot rolling such as temperature, total number of passes, reduction in a pass, etc. have been investigated in a ZnAl eutectoid alloy to obtain finegrained microstructures. Homogenized ingot specimens were hotrolled by a total rolling reduction of 90% with different pass schedule. Microstructural observation on the final sheet showed that nearly equiaxed finegrained microstructure with grain size of about 2µm was formed when the ingot was waterquenched after homogenization.

Abstract: The phase and morphology of precipitates in heat-treated Co-28Cr-6Mo-xC (x = 0.12, 0.15, 0.25, and 0.35mass%) alloys were investigated. The as-cast alloys were solution-treated in the temperature range of 1473 to 1623 K for 0 to 43.2 ks. Complete precipitate dissolution was observed in all four alloys, each of which had different carbon contents. The holding time for complete dissolution was greater for alloys with greater carbon content. The curve representing the boundary between the complete- and incomplete-dissolution conditions for each alloy is C shaped. Under the incomplete precipitate dissolution conditions of the Co-28Cr-6Mo-0.25C alloy, an M23C6 type carbide and a π-phase (M2T3X type carbide with β-Mn structure) were observed at 1548 to 1623 K, and starlike precipitates with a stripe pattern and with a dense appearance were both observed; the former comprised the M23C6 type carbide + γ-phase, and the latter was the π-phase. In contrast, only a blocky-dense M23C6 type carbide was observed at 1473 to 1523 K.