Development of High Strength Metallic Materials Controlled for Nanostructure Using Severe Plastic Deformation

(1)为了使金属材料在高压下发生严重塑性变形，本研究建立了一套高压扭转实验装置。该设备允许在高温下使用圆盘型和圆柱型试件。(2)对Al-3%Mg-0.2%Sc合金进行了HPT。研究了旋转和外加压力对两种试件的硬度和显微组织的影响。硬度随着旋转和施加压力的增加而增加，但两种类型的试件都存在饱和。在样品的外缘，晶粒尺寸减小到0.15μm。高温拉伸试验表明，圆盘形试件的超塑性延伸率为~500%，圆柱形试件的超塑性延伸率为~1600%。(3)经150℃高温拉伸处理后，镁合金的晶粒度从22μm减小到0.22μm，在200℃时的超塑性延伸率为~620%，应变速率为3.3×10^&lt；-3&gt；S^&lt；-1&gt；这一趋势不同于铝合金和镁合金。通过等通道转角挤压(ECA)对时效硬化铝合金进行了SPD试验。ECAP处理的合金在100℃时效后，硬度增加，延伸率均匀增加。当SPD试件在较低温度下进行时效处理时，强度和塑性都有很大的提高潜力。

(1)In this study, a facility for high pressure torsion (HPT) was established in order to impose severe plastic deformation (SPD) on metallic materials under high pressure. This facility permits use of disk-type and cylindrical type of specimens at elevated temperatures for the former type of specimens.(2)HPT was conducted on an Al-3%Mg-0.2%Sc alloy. The effect of rotation and imposed pressure on the hardness and microstructure was examined for both types of specimens. The hardness increased with an increase in rotation and applied pressure but there was a saturation of both types of specimens. The grain size was reduced to 0.15 μm at the outer edges of the specimens. Tensile tests at high temperatures revealed superplastic elongation, of 〜500% for the disk specimens and 〜1600% for the cylindrical specimens.(3)HPT at 150℃ for Mg alloys showed that the grain size was reduced from 22 μm to 0.22 μm which then resulted in a superplastic elongation of 〜620% at 200℃ with a strain rate of 3.3x10^<-3> s^<-1>.(4)A carbon steel processed by HPT exhibited an significant increase in hardness at outer edges of the disk specimens. This trend was different from Al alloys and Mg alloys. Tensile strength of 1.2 GPa was attained from the HPT specimens.(5)Age-hardenable Al alloys were subjected to SPD through equal-channel angular pressing (ECA). Aging at 100℃ for the ECAP processed alloys led to an increase in hardness and also an increase in uniform elongation There was a great potential for an increase in both strength and ductility when SPD specimens are subjected to aging treatment at lower temperatures.