Effect of Isothermal Forging on the Microstructure and Mechanical Properties of Mg-8Gd-3Y-0.5Zr Alloy

Aiming at the problems of poor plastic forming ability,narrow forging temperature range,and strain rate sensitivity of rare earth magnesium alloys,a study on the microstructure and mechanical properties of Mg-8Gd-3Y-0.5Zr alloy with different isothermal forging processes is carried out.The microstructure and properties of the alloy in the as-cast,isothermal forged,and post-aging states after forging are studied with optical microscope(OM),scanning electron microscope(SEM),and tensile testing.The results show that significant dynamic recrystallization occurs during the isothermal forging process,a fine equiaxed grain structure is formed,and the mechanical properties of the alloy are greatly improved.When the isothermal forging temperature is 460℃ and the strain rate is 0.02 s^(-1),the alloy structure performance is the best,the room temperature tensile yield strength(TYS)is 218 MPa,the ultimate tensile strength(UTS)is 299 MPa,and the fracture elongation(FE)is 19.2%.When the alloy is post-forging artificial aged,theα-Mg matrix is dispersed,the Mg_5(Gd,Y)phase is precipitated,the UTS of the alloy is increased to 392 MPa,and the FE is reduced to 12.0%.

Linear Shaped Charge Cutting Property and Charge Cutting Mechanism of Mg-Gd-Y-Zn Alloy

The linear shaped charge cutting technology is an effective technology for aircraft separation.It can separate invalid components from aircrafts timely to achieve light-weight.Magnesium alloy is the lightest metal material,and can be used to cast effective light-weight components of an aircraft construction.However,the application study of the linear shaped charge cutting technology on magnesium alloy components is basically blank.In response to the demand for the linear separation of magnesium alloys,the Mg-12Gd-0.5Y-0.4Zn alloy is selected to carry out the target shaped charge cutting test.The effects of the shaped charge line density,cutting thickness,and mechanical properties on the cutting performance of the alloy are studied.The shaped charge cutting mechanism is analyzed through the notch structure.The results show that the linear shaped charge cutting performance is significantly affected by the penetration and the collapse.The higher the linear density is,the stronger the ability of the linear shaped charge cutter is,and the greater the penetration depth is,which is advantageous.However,the target structure will be damaged when it is too large(e.g.,4.5 g·m^(-1)).Within 12 mm,when the cutting thickness of the target increases,the penetration depth increases.The lower the tensile strength is,the greater the penetration depth is,and the more conducive the penetration depth to the shaped charge cutting is.When the elongation(EL)increases to 12%,the collapse of the target is incomplete and the target cannot be separated.When the tensile strength of the Mg-Gd-Y-Zn alloy is less than 350 MPa,the EL is less than 6.5%,the cutting thickness is less than 12 mm,and the linear shaped charge cutting of the magnesium alloy can be achieved stably.

Effect of Semi-solid Isothermal Heat Treatment on Microstructure of VW63Z Alloy

The effects of isothermal heat treatment on the semi-solid microstructure evolution of VW63Z(Mg-6Gd-3Y-0.4Zr,wt.%)alloy are studied.It shows that the microstructure of VW63Z alloy could transform from equiaxed crystal to semi-solid spherical crystal after isothermal heat treatment above 620℃.With the heating temperature elevating from 620℃ to 635℃ and the holding time prolonging from 10 min to 35 min,the liquid fraction increases gradually.The semi-solid microstructure evolution of VW63Z alloy can be divided into three stages,i.e.,particle coarsening and spheroidization;particle necking,coalescence,and Ostwald ripening;and dynamic equilibrium.The semi-solid process window of VW63Z alloy ranges from 620℃ to 635℃,where the best process parameters are holding at 635℃ for 20 min-30 min.The solid fraction,the average particle size,and the shape factor are 41.1%-53.8%,81.5μm-83.2μm,and 0.70-0.75,respectively.The maximum relative deviations of the solid fraction,the particle size,and the shape factor at different heights of the same billet are 44.6%,17.4%,and 16.6%,respectively,which means that it should pay attention to the uniformity of edge and core of VW63Z alloy during isothermal heat treatment.The driving force of microstructure is supposed to be the reduction of solid-liquid interface free energy.

高Nb-TiAl合金的高温变形行为及其板材的性能

对高Nb-TiAl合金进行多步热压缩,研究其高温变形行为及其板材的性能。结果表明,热压缩变形后高Nb-TiAl合金的组织中等轴γ晶粒和α晶粒的增多、层片晶团的体积分数和尺寸降低,使其变形能力提高。根据这些结果确定了最优轧制工艺为应变速率低于0.5 s^(-1)、道次变形量前期应不高于25%、变形温度高于1150℃。选用上述工艺对其其进行5道次大变形量轧制,制备出表面质量良好、无缺陷的高Nb-TiAl合金板材,其尺寸为600 mm×85 mm×3 mm。这种板材具有双态组织,平均晶粒尺寸小于5μm,其室温屈服强度、抗拉强度和塑性分别为948 MPa、1084 MPa和0.94%,800℃下抗拉强度为758 MPa。