LC4超硬铝合金大变形热扭转时微观组织的演变机制

具有尺寸超过100μm粗大原始组织的LC4超硬铝合金在446℃和0.018rad/s角速度条件下扭转变形，微观组织逐渐细化至约10μm并获得超塑性，微观组织的细化并非通过新晶粒形核和长大的非连续动态再结晶过程，而是通过位错向亚晶界聚集使亚晶界位向差逐渐增大，界面性质逐渐从亚晶界转变为晶界的连续再结晶过程。     

Ti－6Al－4V及Ti－10V－2Fe－3Al合金超塑性变形中各向异性研究

对Ｔｉ－６Ａｌ－４Ｖ挤压管材和厚板以及Ｔｉ－１０Ｖ－２Ｆｅ－３Ａｌ合金板材进行了拉伸和压缩实验，以考察其超塑性变形中的各向异性。这些钛合金超塑变形中的各向异性主要体现在以下几个方面：（１）超塑拉伸或压缩中圆试样横截面变为椭圆形状；（２）由材料不同方向截取的试样在超塑拉伸或压缩中应力一应变速率关系不同；（３）横向试样超塑拉伸中试样表面凹凸不平并逐渐发展为多颈缩。这些各向异性表现，主要与材料原始显微组织及其在变形中的演变相关。本文并对已有的描述各向异性超塑变形的本构方程进行了修正。     

DIFFUSION BONDING OF SUPERPLASTIC AI ALLOY LC4

Diffusion bonding of supcrplastic Al alloy LC4,with prior surface treatment of organicsolution protecting coating after electroplishing and stainless steel wool brushing,wasperformed by Gleeble test machine under conditions ranged 490—530 ℃,1.0—3.0 MPa.30—180 min and vacuum of 1.0×10~(-3) Pa.The joints were examined to have similarstrength and microstructure to the base metal Discussion was made on the effect ofsuperplastic treatment on bonding.The micromechanism for diffusion bonding of super-plastic metal was suggested as the migration of original bond interfaces caused by atomicdiffusion and grain growth. Experimental results for the alloy as quench-aged state werepresented to compare with the superplastic one.     

SUPERPLASTICITY OF A RAPIDLY SOLIDIFIED AI-Li ALLOY

A rapidly solidified microcrystalline Al-Li-Cu-Mg-Zr alloy and its superplasicity have beeninvestigated.An optimum tensile elongation of 585% was obtained at 540℃ and strain rate1.67×10~(-2)s~(-1).The superplastic Al-Li alloy is manufaetured using thermomechanical pro-cessing:solution,overaging,warm rolling and recrystallization.Microstructural changes inthermomechanical processing and cavitation occurred during superplastic deformation havebeen observed.The superplastic failure of alloy may be caused mainly by nucleation andgrowth of cavities as well as the linkage around grains.     

半球形Al-Mg-Sc合金超塑胀形壁厚分布的有限元分析

应用MARC软件对半球形Al-Mg-Sc合金的超塑胀形进行仿真,分析了正反向超塑胀形对于半球形件壁厚分布的影响,以及不同深度的凹模对胀形结果的影响。结果表明,采用合理的正反胀形可以很好地改善成形件的厚度不均匀性,试验验证了仿真和试验结果比较吻合。     

SiCp增强2024铝基复合材料超塑性的研究

对搅拌铸造法制备的SiCp/2024Al复合材料超塑性的预处理、力学行为、微观结构及变形机制进行了研究,结果表明,合适的强烈塑性变形是改善复合材料组织进而提高超塑性的有效方法:经小挤压、热轧和冷轧后,在温度为823K、初始应变速率为 1.1×10-3 s-1的拉伸变形条件下,超塑延伸率为405%,超塑变形机制为晶粒的适度长大、动态连续再结晶和适当的微量液相共同协调的晶界滑动:液相不是该复合材料展现超塑性的必要条件。     

供应态LC9铝合金的超塑性试验研究

通过拉伸实验研究了供应态LC9铝合金经退火处理后的超塑性变形特性。在初始应变速率3.3×10-4s-1,拉伸温度410～510℃时,合金均具有超塑性,平均伸长率为106%～181%。最佳超塑性温度为450℃,最佳初始应变速率为3.3×10-4s-1,在此温度和应变速率条件下,合金平均伸长率达到181%,m值为0.41,流动应力仅为14.4MPa。显微组织和断口观察表明,在超塑性变形过程中发生了明显的动态再结晶,再结晶晶粒等轴、细小、均匀。空洞在晶界处形核、长大,最后连接,导致试样断裂。     

板料超塑性拉伸失稳研究

基于板料超塑性变形的特点，本文将超塑性变形全过程分为稳定变形、准稳定变形、应变路径漂移和集中性失稳发展四个阶段，依据增量理论，用数值方法建立了一普遍适用的失稳模型。然后在此基础上，依板料发生集中性失稳（ｄε＿２＝０）为许用变形程度的极限，预测了板料超塑变形时的成形极限曲线。对铝合金ＬＹ１２ＣＺ和半硬态黄铜Ｈ６２的超塑性实验研究表明：用本文提出的失稳模型预测的超塑性板料的成形极限与实验结果具有较好的一致性。     

Ti－6Al－4V及Ti－10V－2Fe－3Al合金超塑性变形中各向异性研究

对Ｔｉ－６Ａｌ－４Ｖ挤压管材和厚板以及Ｔｉ－１０Ｖ－２Ｆｅ－３Ａｌ合金板材进行了拉伸和压缩实验，以考察其超塑性变形中的各向异性。这些钛合金超塑变形中的各向异性主要体现在以下几个方面：（１）超塑拉伸或压缩中圆试样横截面变为椭圆形状；（２）由材料不同方向截取的试样在超塑拉伸或压缩中应力一应变速率关系不同；（３）横向试样超塑拉伸中试样表面凹凸不平并逐渐发展为多颈缩。这些各向异性表现，主要与材料原始显微组织及其在变形中的演变相关。本文并对已有的描述各向异性超塑变形的本构方程进行了修正。     

Low-temperature superplasticity of ZK40 magnesium alloy processed using equal channel angular pressing

Microstructure evolution and superplastic behaviors of ZK40 magnesium alloy were investigated in the temperature range of 473～623 K. Transmission electron microscopy (TEM) was used to study the microstructure changes, twinning occurred significantly after being processed by equal channel angular pressing (ECAP) for one pass through the die, the mean grain size was 5.6μm. Finer grains can be obtained after further processing through ECAP, the average grain size of the alloy processed by ECAP for three passes was as low as 0.8 μ_m; this alloy exhibited low temperature superplasticity at 473～523 K, elongations obtained at the same initial strain rate of 1×10~(-3) s~(-1) were 260％ at 473 K and 612％ at 523 K, respectively. Corresponding values for the ZK40 alloy processed by ECAP for only one pass were 124％ at 473 K and 212％ at 523 K, respectively; poor superplastic behavior of this material was related to the long-range stresses associated with the non-equilibrium grain boundaries within the coarse grains. The incompatibility between fine and coarse grains was thought to be unfavorable to the improvement of superplasticity.