A directionally solidified TWIP steel (Fe-25Mn-2.5Al-2.5Si) was prepared by liquid metal cooling technology. The microstructure and mechanical behavior were examined and compared with usually solidified samples. The directionally solidified TWIP steel shows a typical columnar grain structure, and the maximum true stress and true strain along the longitudinal direction of the sample are 1060MPa and 71% respectively. As a comparison, the usually solidified samples shows an equiaxed grain microstructure with the maximum true stress and true strain of only 994MPa and 58%, respectively. Moreover, the two solidification modes also lead to very different strain hardening behavior, particularly in the changes of strain hardening rate with strain. This suggests that the grain boundary plays a key role in the mechanical properties of TWIP steels, and changing the grain boundaries can be effective to improve the comprehensive mechanical properties of TWIP steels.
In this study, Strontium (Sr) was added as modifier during the casting of Al-11.6Si-0.5Mg alloy, and the effect of T6 heat treatment on microstructure and performance of alloy was also investigated. The results showed that the 0.3% Al-8%Sr master alloy can refine effectively the α-Al dendrite and eutectic structure; the best economic process of T6 heat treatment is solution at 535°C for 6 hrs., and water cooling at 50~60°C,aging at 160°C for 6 hrs , then air cooling. After Sr modification and T6 heat treatment, the mechanical properties of alloy are improved remarkably, i.e., the tensile strength increased to 348MPa from 183MPa before modification and the elongation raises from 3.0% to 6.5%. So this alloy is applied to the strain clamp products in electric power fitting industry.
Foam magnesium alloy was an idea substitute of hard tissue of human bodies because its elasticity module was close to the bone of human. In the paper, foam degradable magnesium alloys were prepared by “Press-Dissolution-Vacuum sintering-Hot treatment-Aging” powder manufacturing process firstly. Then samples were coated by immersion in a bath containing phosphate and rare earths lanthanum. Results show that, Mg-0.9Mn foam magnesium alloys after hot treatment had better anticorrosion performance; and coated foam magnesium alloys form the bath with phosphate lanthanum chloride had lower rate of degradation.
An Al coating and black passive film technique was developed in this research. Meanwhile, a fine and uniform Al coating with good binding force on steel surface was prepared. And a black passive film was used as a post-treated film of the electroplated Al coating. The result proves that the corrosion resistance of electroplated Al coating was over one time higher than that of zinc coating by black passivation. Besides, Al coating was less brittle with good ductility and, it could be used as a pretreatment layer before conducting laser heat treatment to significantly improve the efficiency of laser heat treatment.
One kind of deformed magnesium alloy with high strength and high plasticity was made to be bicycle parts. Meantime, the microstructure and mechanical properties of the magnesium alloy were analyzed. In addition, the deformation and welding technology of taper pipe and shaped tube of bicycle were studied. The results showed that the bicycle parts manufactured through extruding and welding of the new type magnesium alloy have high strength, good plasticity. The tensile strength can reach 321.3 MPa and the elongation is more than 20%. By adopting the new welding process of internal mending and cuttage grafting, the after-welding-strength is 90.2%. of the base metal Meanwhile, the industrialization level can meet the requirements of European Union (EU) vehicle standards.
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