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%.

Repair Welding of Casting Magnesium Alloys:A Review

Magnesium (Mg) alloys have broad application prospects in the fields of aerospace,national defense,and military industries,owing to their advantages of high specific strength and stiffness,good damping properties,and excellent castabilities. However,defects such as oxidation inclusions,shrinkage cavities and porosities,and hot cracks are readily generated in Mg alloy components,which seriously reduce the performance stability of the products. Related repair welding technologies for Mg alloys can greatly reduce the rejection rate and production cost,and exhibit significant value in scientific research and engineering application. In this review,the weldability of Mg alloys is introduced firstly according to their physical and chemical properties. Then,various repair welding technologies and pre-weld treatments applicable to Mg alloys are systematically summarized,and the effects of welding parameters as well as heat treatments on the microstructure and performance of the repaired joints are clarified. Finally,the existing problems and development trends of repair welding technologies for Mg alloys are summarized based on the actual engineering application requirements.

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.

Applications of Magnesium Alloys in Aerospace and Aviation

Magnesium alloys are well applied in aerospace and aviation because of their mass saving potential,good electromagnetic shielding performance,and high damping capacity. To further promote the applications,in this paper,the applications of magnesium alloys are reviewed,which could provide insights for researchers and application designers. Firstly,the applications in aerospace are reviewed,including missile,satellite,rocket,and spacecraft.Secondly,the applications and commercial magnesium alloys in aviation are summarized. Thirdly,the bottleneck and existing problems for such magnesium alloys applied in aerospace and aviation are discussed. The requirements for the magnesium alloy performance in aerospace and aviation are evaluated and elaborated.

航天先进轻合金材料及成形技术研究综述

轻合金是现代航天装备轻量化首选材料,高性能轻合金构件制造能力决定了我国航天装备的功能水平与竞争力。为推动先进轻合金材料及成形技术在航天领域的应用,对高性能轻合金材料、铸造、钣金成形、增材制造等技术领域在基础理论、工艺开发、装备研制、工程应用等方面的发展现状进行了梳理,提出了高强耐热铸造镁合金材料、高性能钛铝合金材料、高性能镁合金熔模精密铸造、数字化铸造、旋压成形、超塑成形、钛/铝合金电弧熔丝增材制造等相关技术的后续发展方向。

高强韧稀土镁合金大型复杂铸件制造技术研究现状及展望

在介绍高强韧稀土镁合金(Mg-RE)大型复杂铸件研制技术瓶颈的基础上,指出了制造过程中熔体纯净化/细化孕育与熔体纯净化/成分均匀化之间的相互制约以及铸件本体强韧性不足的影响因素,综述了国内外稀土镁合金熔体纯净化、细化孕育、均匀化、凝固组织模拟与调控、缺陷抑制、热处理组织调控等技术的研究现状。明确了未来研究需要关注的两大科学问题:解决大熔量稀土镁合金熔体“均匀化-纯净化-细化孕育”冶金交互作用机理,稀土镁合金大型复杂铸件“溶质场-流动场-能量场”传输规律及其对组织和缺陷演变的影响机理。

低溶质总量高强镁合金复杂铸件本体性能优化

基于溶质总量控制开展Mg-RE系合金成分设计,筛选出抑制镁合金离异共晶相比例的元素,研究合金成分对铸造镁合金非平衡凝固组织、凝固区间、流动性、抗裂能力的影响,且基于筛选成分组织优化了热处理工艺。结果表明,在砂型慢冷条件下采用Mg-5.8Gd-3.0Y-0.4Zr制备的大型复杂结构件本体力学性能优异,抗拉强度≥300 MPa,屈服强度≥220 MPa,伸长率≥3%,可满足大型复杂结构件大载荷、大过载的使用工况。

VW63Z铸造镁合金线型分离性能及切割机理研究

针对航天飞行器领域对镁合金线型分离特性的需求,开展了VW63Z镁合金聚能切割性能研究。对不同力学性能的VW63Z镁合金试板进行线型分离切割试验,研究了抗拉强度和伸长率对聚能切割性能的影响,并分析了线型聚能切割机理。研究表明,力学性能通过影响试样的侵彻深度来影响材料的线型分离性能。镁合金伸长率小于6%时,抗拉强度对线型分离性能的影响较弱,而伸长率严重影响着线型分离性能。随着伸长率增加,切割分离试板的侵彻深度逐渐降低,不利于材料的线型聚能切割分离。当材料伸长率小于6.5%,抗拉强度小于352MPa时能稳定实现7.2mm切割厚度镁合金试板的线型切割分离。

Mg-Y-Gd-Sm系铸造镁合金的显微组织和力学性能

针对生产中稀土镁合金低成本化,结合溶质总量控制与稀土耦合强化原理,设计了3种Mg-Y-Gd-Sm镁合金。结合DSC曲线和铸态组织分析3种合金离异共晶相占比;对比分析3种合金不同固溶处理后的组织及力学性能和不同温度的时效硬化曲线,以优化固溶及时效热处理工艺。结果表明,在砂型慢冷条件下Mg-4.5Y-2.5Gd-1.5Sm合金经530℃×24 h+200℃×100 h(T6)处理后,力学性能最优,抗拉强度、屈服强度、伸长率分别为267 MPa、200 MPa、2.0%。

Mg-3Y-3Gd(-0.5Zn)铸造镁合金的显微组织和力学性能

基于合金低成本化及“固溶强化增塑”的合金设计理念,以及航空航天大型复杂构件的砂型铸造条件,设计并对比研究了Mg-3Y-3Gd和Mg-3Y-3Gd-0.5Zn合金的微观组织及力学性能的演变。结果表明,两种合金铸态组织晶粒细小,无大块离异共晶相存在;Zn的加入引入了LPSO相,从而提升了强韧性。两种合金时效强化能力较弱,但Mg-3Y-3Gd-0.5Zn合金经500℃×24 h+200℃×50 h的T6处理后,其抗拉强度、屈服强度达到224 MPa、126 MPa,伸长率为21.2%,在要求高塑性的镁合金构件中有良好的应用潜力。

含Er铸造镁合金材料研究现状及展望

在介绍国内外含Er铸造镁合金研究进展的基础上,分析了Er在镁合金熔体净化、组织与性能优化方面的作用,构建了含Er稀土镁合金固溶度变化简易模型,讨论了含Er镁合金的强化机理与耐蚀机理,对含Er铸造镁合金的未来发展方向进行了展望。