Ca含量和流变挤压铸造工艺参数对AZ91−1Ce−xCa合金显微组织和力学性能的影响

首先,研究不同Ca含量AZ91−1Ce合金的显微组织、力学性能和阻燃性能,优化出最佳Ca含量。然后,系统研究流变挤压铸造工艺参数(包括压力和转速)对AZ91−1Ce−2Ca合金显微组织和力学性能的影响。结果表明,随着Ca含量的增加,AZ91−1Ce−xCa合金的显微组织细化,阻燃性能提高。但当Ca含量超过1%(质量分数)时,随着Ca含量的增加,AZ91−1Ce−xCa合金的力学性能迅速降低。在流变挤压铸造工艺中,压力和转速增加使AZ91−1Ce−2Ca合金的组织明显细化,气孔率降低,力学性能提高。与常规铸造相比,添加2%Ca(质量分数)的AZ91−1Ce合金经流变挤压铸造成形后,不仅保证合金的抗氧化性(801℃),而且提高其力学性能。

Effect of stainless steel fibers on properties of MgO-C refractories

MgO-C refractories with stainless steel fibers were prepared to investigate the effects of stainless steel fibers addition on the thermal shock resistance,oxidation resistance,and microstructure of MgO-C refractories,and the optimum amount of stainless steel fibers was determined.The results showed that adding stainless steel fiber in MgO-C refractories can increase flexural strength and thermal shock resistance,with an optimal addition of 2 wt.%,owing to the bridging effect and crack deflection toughening of stainless steel fibers inside the material.The formation of MgAl1.9Fe0.1O4 composite spinel,which was responsible for higher oxidation resistance,produced volume expansion and prevented the diffusion of oxygen.The strengthening mechanism is physical embedding at room temperature,while it is reaction bonding at high temperature.

Strain-controlled fatigue characteristics of a cast Mg-Nd-Zn under peak-aged and over-aged conditions

Strain-controlled fatigue characteristics of peakaged and over-aged Mg_(96.47)Nd_(2.9)Zn_(0.21)magnesium alloys containing 0.42Zr,including stress response,strain resistance,hysteresis loops,strain-life and corresponding lowcycle fatigue life prediction model,were studied.In the peak-aged state(T61:540℃×8 h+200℃×14 h),the alloy shows higher cyclic stress response,but lower ductility than the alloy in the over-aged state(T6_(2):540℃×8 h+200℃×400 h).The yield strength and ultimate tensile strength of the alloy under T6_(1)-and T6_(2)-treated conditions are close.Compared with T6_(1)-treated alloy,the steady stress amplitude occurred in T6_(2)-treated alloy is due to higher ductility and more homogenous deformation.In T6_(1)state,the fatigue cracks in the alloy first initiate along the cracked persistent slip bands and then propagate in the trans-granular mode,while in the T6_(2)state,the fatigue cracks initiate along grain boundaries and then propagate in the inter-granular mode.

Development of High Strength and Toughness Non-Heated Al–Mg–Si Alloys for High-Pressure Die-Casting

Based on the 3 factors and 3 levels orthogonal experiment method,compositional effects of Mg,Si,and Ti addition on the microstructures,tensile properties,and fracture behaviors of the high-pressure die-casting Al-x Mg-y Si-z Ti alloys have been investigated.The analysis of variance shows that both Mg and Si apparently infl uence the tensile properties of the alloys,while Ti does not.The tensile mechanical properties are comprehensively infl uenced by the amount of eutectic phase(α-Al+Mg2Si),the average grain size,and the content of Mg dissolved intoα-Al matrix.The optimized alloy is Al-7.49 Mg-3.08 Si-0.01 Ti(wt%),which exhibits tensile yield strength of 219 MPa,ultimate tensile strength of 401 MPa,and elongation of 10.5%.Furthermore,contour maps,showing the relationship among compositions,microstructure characteristics,and the tensile properties are constructed,which provide guidelines for developing high strength and toughness Al–Mg–Si–Ti alloys for high-pressure die-casting.