Lin Geng

Evaluation of the microstructure of in-situ reaction processed Al3Ti-Al2O3-Al composite

Abstract 1. 1. Differential thermal analysis (DTA) of squeeze-cast TiO2/Al bulk indicates that an exothermic reaction occurs after the aluminium melts. A high temperature combustion synthesis process was achieved to produce a fully dense Al3Ti + α-Al2O3+ Al in situ composite. 2. 2. Very fine-scale dispersion of the Al3Ti and α-Al2O3 reinforcing phases, ranging from 0.4 to 1.0μm, was obtained in the Al matrix. The Al3Ti phase, some containing Al2Ti precipitates, form in the shape of block and whisker. The nanometer scale α-Al2O3 particles are found near the Al3Ti phase and in the Al matrix, and, occasionally, within the Al3Ti phase. 3. 3. Analysis of the microstructural evolution indicates that the in situ processing involves two steps: (1) a reaction process between the molten aluminium and TiO2 to produce alumina particulates and liquid Ti. (2) a subsequent solidification process of remained Al and Ti displaced from the reaction with decreasing temperature to produce Al + Al3Ti blocks and then the smaller Al3Ti precipitates form as the solidcools.

Investigation of high-temperature deformation behavior of a SiC whisker reinforced 6061 aluminium composite

Abstract The high-temperature deformation behavior of silicon carbide whisker reinforced 6061 aluminium alloy composite has been studied by means of compressive tests. The experimental results have shown that the critical reduction of the SiC w /6061Al composite (the value of the compressive deformation that causes sample cracking) increases with increase of the deformation temperature and decreases with increase in the deformation ratio. There is a peak in the compressive stress-strain curves of the SiC w /6061Al composite, which is caused by whisker rotation rather than being a sign of recrystallization.

Effects of Mg content on microstructure and mechanical properties of SiCp/Al-Mg composites fabricated by semi-solid stirring technique

10% (volume fraction) SiC(subscript p)/Al-Mg composites with different Mg contents were successfully fabricated by semi-solid mechanical stirring techruque under optimum processing conditions. Effects of Mg content on microstructure and mechanical properties were studied by scanning electron microscopy (SEM), X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The results indicate that SiC particles disperse homogeneously in Al-Mg matrix and interfacial reaction between Al matrix and SiC particles is effectively controlled. Distribution of SiC(subscript p) reinforcement and interfacial bonding are improved by adding Mg. Additionally, the mechanical properties of composites are remarkably improved with the Mg content increasing.

Improving the corrosion resistance of Mg–4.0Zn–0.2Ca alloy by micro-arc oxidation

In this paper, corrosion resistance of the Mg-4.0Zn-0.2Ca alloy was modified by micro-arc oxidation (MAO) process. The microstructure and phase constituents of MAO layer were characterized by SEM, XRD and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of MAO treated Mg-4.0Zn-0.2Ca alloy in the simulated body fluid were characterized by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The microstructure results indicated that a kind of ceramic film was composed by MgO and MgF2 was formed on the surface of Mg-4.0Zn-0.2Ca alloy after MAO treatment. The electrochemical test reveals that the corrosion resistance of MAO treated samples increase 1 order of magnitude. The mechanical intensity test showed that the MAO treated samples has suitable mechanical properties.

Compression testing of a SiCw/Al composite at temperatures close to and above the solidus of the matrix alloy

Hot compression behaviour of a 20 vol.% SiCw/6061Al composite was determined at temperatures close to and above the solidus of the matrix. Work hardening behaviour of the composites was analyzed by whisker redistribution and breakage during deformation. Temperatures above the solidus of the matrix were suggested for the plastic forming of the composites.

Microstructure and properties of SiCw/6061 aluminium alloy composites after compression at temperatures around solidus of matrix

Abstract The effect of compressive deformation at temperatures around the solidus of the matrix on the microstructure and properties of SiCw/6061 aluminium alloy composites was investigated. It was found that the temperature, strain rate, and amount of deformation affect whisker distribution and breakage, densification and uniformity of composites, and SiCw/matrix alloy interfacial bonding. The microstructural evolution due to compression affects the properties of the composites, which is considered to be the most important aspect for evaluating high temperature plastic forming of the composites. The optimum parameters for compressive deformation were determined by analysing the microstructure and the properties of the composites.

Effects of stirring parameters on microstructure and tensile properties of (ABOw+SiCp)/6061Al composites fabricated by semi-solid stirring technique

Abstract Aluminum borate whisker (ABO w ) and silicon carbide particle (SiC p ) hybrid reinforced 6061Al matrix composites ((ABO w +SiC p )/6061Al) were fabricated by semi-solid mechanical stirring technique with different stirring temperatures and different stirring time. The influence of stirring parameters on microstructure and mechanical properties of the composites was investigated using scanning electron microscopy (SEM), X-ray diffractometry (XRD), transmission electron microscopy (TEM) and tensile tests. The results reveal that the homogeneity of reinforcement and tensile properties increase with decreasing the stirring temperature and increasing the stirring time. The optimal stirring parameters of 640°C and 30 min are exploited based on the microstructure observation and tensile properties of the composites.

Microstructural evolution and enhanced superplasticity in friction stir processed Mg–Zn–Y–Zr alloy

[Xie, G. M.; Ma, Z. Y.; Chen, R. S.] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China. [Xie, G. M.; Geng, L.] Harbin Inst Technol, Sch Mat Sci & Engn, Harbin 150001, Peoples R China.;Ma, ZY (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China;zyma@imr.ac.cn

Continuous cooling transformation behavior of Alloy 718

Abstract The transformation behavior of Alloy 718 is affected significantly by the cooling rate. The γ″-phase appears at cooling rates less than 20 °C/min and δ-phase appears at grain boundaries as well as the MC type carbides at cooling rates below 5 °C/min. The δ-phase nucleates and grows preferentially at grain boundaries, and less preferentially at the MC carbides. The size of the γ″ and δ-precipitates increases consistently with decreasing cooling rate for the given conditions. The hardness varies with the transformation behavior. A hardness peak was noticed for a cooling rate of 5 °C/min. The hardness peak corresponded to the maximum volume fraction of γ″ which in turn was strongly affected by the presence of the δ-phase.

Partial recrystallization in the nugget zone of friction stir welded dual-phase Cu–Zn alloy

For single and quasi-single phase metallic materials, complete dynamic recrystallization has been observed in the nugget zones (NZs) of friction stir welds (FSWs), producing fine and uniform equiaxed grains. In this study, partial dynamic recrystallization was observed in the NZ of 5 mm thick friction stir welded brass plates. Whereas the top and the advancing side of the NZ were characterized by fine completely-recrystallized grains, the remaining region consisted of coarse non-recrystallized deformed grains, annealed recrystallized grains and deformed recrystallized grains. The occurrence of partial recrystallization was attributed to the inhibiting effect of a high volume fraction of fine β′-phase particles. Increasing the FSW passes reduced the fraction and size of non-recrystallized deformed grains, but could not eliminate the partially recrystallized zone completely.