Advanced Materials Research Vols. 284-286

Abstract: Tensile behaviors of extruded and rolled AZ80 Mg alloy were investigated with elongation-to-failure tensile tests at constant temperatures of 300 °C, 350 °C, 400 °C, and 450 °C, and constant strain rates of 10^-2 s^-1 and 10^-3 s^-1. Experimental data show that the material exhibits tensile ductilities of over 100% at 400 °C and 450 °C, featured by long steady state deformation. Microstructure studies show that annealed coarse grains were remained in the gauge region during the tensile tests, and the enhanced tensile ductilities resulted from dislocation creep, other than dynamic recrystallization or grain boundary sliding. Cavity evolution and recrystallized coarse grains near fracture end caused premature failure of the material.

Abstract: Tensile behaviors of extruded and rolled AZ80 Mg alloy were investigated with elongation-to-failure tensile tests at constant temperatures of 300 °C, 350 °C, 400 °C, and 450 °C, and constant strain rates of 10^-2 s^-1 and 10^-3 s^-1. Experimental data show that the material exhibits tensile ductilities of over 100% at 400 °C and 450 °C, featured by long steady state deformation. Microstructure studies show that annealed coarse grains were remained in the gauge region during the tensile tests, and the enhanced tensile ductilities resulted from dislocation creep, other than dynamic recrystallization or grain boundary sliding. Cavity evolution and recrystallized coarse grains near fracture end caused premature failure of the material.

Abstract: Hardening problems in thermoplastic materials are presented. The examples of thermo-diffusive hardening are analyzed. Theoretical considerations are recalled to determine the combined effects of thermoplasticity with thermo-diffusion term considering gradients in interstitial concentration, in solvent composition, in stress and in temperature.

Abstract: The influences of RE and P complex modifications on microstructures and wear-resistance of hypereutectic Al-24Si alloy were studied. The results show that the complex modifications of P and RE make the coarse block primary crystal silicon refined and their edges and angles are passivated, the large needle-like network eutectic silicon be modified to the fine lamella or particle ones. The optimum modification effect occurs with 0.10%P and 0.9%RE. The complex modification of P and RE can also obviously improve wear resistance of hypereutectic Al-24Si alloy. When the tested alloys modified with 0.10%P and 0.9%RE, the optimal wear resistance of modified alloys is obtained. The weight loss is decreased to 3.9mg from 5.4mg of the unmodified alloy, decreased by 27.8%. The abrasive wear caused by the breaking of Si phase is dominant wear mechanism of the alloy. It can be attributed to the refinement of primary silicon and eutectic silicon particles and the increase of strength and ductibility of alloys caused by the complex modification of P and RE.

Abstract: The effects of melting process on Zr content and grain size in ZE41A alloy were investigated in this study. The results show that the soluble Zr increases with the increased addition content of Mg-Zr master, up to 0.87%. The ratio of Zr addition content to soluble Zr content changes within 3.86-4.8. The melt temperature has little effect on soluble Zr content. Grain size grows and both soluble Zr and total Zr decrease with the prolonged isothermal holding of the melt.

Abstract: Recently spark plasma sintering has been proven to be effective non-traditional powder metallurgy technique to sinter fully dense materials in short sintering times at relatively low sintering temperatures and without a binder or pre-compaction step. Despite the importance of aluminum based alloys as candidate materials for applications in aerospace and automotive industries because of their light weight, very little work was dedicated to spark plasma processing of these materials. In this work we explored the possibility to process Al2124 and Al6061 alloys using spark plasma sintering technique. The sample were sintered for 20 minutes at 400, 450 and 500°C using fully automated FCT system spark plasma sintering equipment. A scanning electron microscope was used to analyze the microstructure of sintered samples. The density and Vickers microhardness of the sintered samples were measured using an electronic densimeter and a digital microhardness tester respectively. The hardness and density of the spark plasma sintered samples were reported as a function of sintering temperature. It was found that full density (100 % of the theoretical density) was achieved with sintering for 20 minutes at 450°C for Al6061 alloy and at 500°C for Al2124 alloy. The density and microhardness of the sintered samples increased with the increase of sintering temperature.

Abstract: In this paper, the Al-Zn-Sn-Ga anode alloy was quenched from 460 °C. The influences of corrosion time and different microstructure of the alloy on its corrosion morphology were investigated to clarify the effect of quenching on the corrosion morphology of the alloy. The inhomogeneous composition in the as-cast alloy directly caused various corrosion potential in the alloy and that the driving force of corrosion was different. Lots of circular corrosion pits and basic uniform composition were observed in the quenching sample. The results reveal that the corrosion morphology of the anode alloy is affected by quenching treatment employed.

Abstract: The ZM5-0.1%RE magnesium alloy was heated to 800°C, when the surface oxide film was formed, the ZM5-0.1% RE Magnesium alloy which had being oxidized obtained by removing the surface oxidation film on the ZM5-0.1%RE magnesium alloy at room temperature. TGA curve, oxidaxion kinetics curves at constant temperatuers of the alloy and XRD spectrum of the surface film were analyzed in order to investigate the sureface oxidation behavior.The results show that the alloy still has anti-oxidation performance, And the oxide inerease occurred mostly between 400°C and 700°C，a layer of tight oxide film with 4-5.5um and composed of RE₂O₃, MgO, Al₂O₃ and Mg₁₇Al₁₂ was formed on the surface of magnesiurn alloy. The tight surface oxide film prevented the further oxidation of the base magnesiurn alloy, It show that the regeneration ability of oxidation film on ZM5-0.1%RE Magnesium Alloy was good.

Abstract: The tensile properties at strain rates of 0.001/s, 0.1/s and 0.6/s for Mg-3Al1-Zn-2Y, Mg-3Al-2Zn-2Y and Mg-3Al-6Zn-2Y were researched, which showed great difference on the mechanical sensitivity to strain rate. The fractal behavior of the alloys’fracture interface is remarkable. The brittleness, plasticity and the appearance of fracture interface can be related through the fractal dimension D.

Abstract: This paper presents the study of the influences of cooling holes on the creep life behavior in the modeling specimen of single crystal cooling turbine blade at high temperature. Thin-walled cylindrical specimens with holes are tested to model the air-cooled turbine blade. Specimens without holes are also studied to make comparisons. Experimental results show that at 900°C, the creep lives of specimens with holes are longer than those of specimens without holes. Scanning Electron Microscopy (SEM) analyses reveal that creep deformations occur firstly around the cooling holes and finally rupture at the region with low stress and strain. Finite element analyses are used to study the creep damage development by a K-R damage model which has been implemented into the Abaqus user subroutine (UMAT). Simulation results show that stress concentration and redistribution occur around the cooling holes during the creep development. It is also shown that the maximum strain and stress are around the cooling holes which are the initial rupture region in the experiments.