Effect of scandium on superplasticity of Al-Mg alloys

1　ＩＮＴＲＯＤＵＣＴＩＯＮＡｌ Ｍｇ Ｓｃａｌｌｏｙ ｐｏｓｓｅｓｓｅｓｈｉｇｈｓｔｒｅｎｇｔｈ ,ｈｉｇｈｔｏｕｇｈｎｅｓｓ,ｌｏｗｅｒｄｅｎｓｉｔｙ,ｇｏｏｄｗｅｌｄａｂｉｌｉｔｙａｎｄｃｏｒ ｒｏｓｉｏｎｒｅｓｉｓｔａｎｃｅ[1 ,2 ] .Ａｐｐｌｙｉｎｇｔｈｅｓｕｐｅｒｐｌａｓｔｉｃｉｔｙｏｆｔｈｅｓｅａｌｌｏｙｓｔｏｆｏｒｍｉｍｐｏｒｔａｎｔｃｏｍｐｌｅｘｐａｒｔｓｆｏｒｔｈｅｓｐａｃｅｃｒａｆｔｉｓａｓｉｇｎｉｆｉｃａｎｔｒｅｓｅａｒｃｈｓｕｂｊｅｃｔａｔｐｒｅ ｓｅｎｔ[3 ,4] .Ｔｈｉｓｒｅｓｅａ…     

High strain rate superplasticity of rolled AZ91 magnesium alloy

The high strain rate superplastic deformation properties and characteristics of a rolled AZ91 magnesium alloy at temperatures ranging from 623 to 698 K（0.67Tm-0.76Tm） and high strain rates ranging from 10^-3 to 1 s^-1 were investigated.The rolled AZ91 magnesium alloy possesses excellent superplasticity with the maximum elongation of 455% at 623 K and a strain rate of 10-3 s-1,and its strain rate sensitivity m is high up to 0.64.The dominant deformation mechanism responsible for the high strain rate superplasticity is still grain boundary sliding（GBS）,and the dislocation creep mechanism is considered as the main accommodation mechanism.     

Al-6Mg-0.2Sc合金高应变速率超塑成形性能

在温度400～500℃、初始应变速率为2.0×10-4～2.0×10-2 s-1的条件下,对Al-6Mg-0.2Sc合金冷轧板材(初始晶粒尺寸为25μm)进行了相应的超塑性能、高应变速率超塑性胀形成形实验研究.结果表明:在450℃、初始应变速率为2.0×10-2s-1的实验条件下,Al-6Mg-0.2Sc合金冷轧板材具有高应变速率的超塑性能,其最大延伸率为421%;在高应变速率条件下,胀形成形大端直径为d154 mm,深度h为80 mm的锥形零件的成形时间为73 s,成形后零件的壁厚变薄的不均匀率小于8%.此外,还对成形零件的微观组织进行了初步的SEM观察分析.结果表明,成形零件的微观组织无明显粗化,其孔洞率小于1.5%.     

Al-Mg合金动态再结晶诱发超塑性时的空洞行为

在Ａｌ－Ｍｇ合金超塑变形过程中,发现了一类反常的空洞演化规律,也就是空洞随真应变的增加而呈现“波浪型”的演化规律。通过对微观组织特征和力学性能曲线的综合分析,认为这种特殊的空洞演化规律,主要是动态再结晶所致,也就是动态再结晶对空洞生长具有抑制作用。通过对空洞形貌的定量图像分析,还得到了新的空洞演化模型。     

High strain rate superplasticity in an Al–Mg–Sc–Zr alloy subjected to simple thermomechanical processing

Superior superplastic ductility of 2300% was achieved at 520 °C and  s⁻¹ in an Al–5%Mg–0.2%Sc alloy produced by traditional chill casting followed by cold rolling with a total reduction of 80%.     

MB2/SiC复合材料的高应变速率超塑性

用搅拌法制备了以MB2为基、以SiC颗粒为增强体的镁基复合材料 ,铸锭在 390℃热挤压成棒材。在温度为 380～ 560℃和应变速率为 2 .0 8× 1 0 - 3s- 1 ～ 5 .2 1× 1 0 - 1 s- 1 的范围内 ,测试了挤压态MB2 / 1 0 %SiC(体积分数 )和MB2 / 5 %SiC镁基复合材料的超塑性。MB2 / 1 0 %SiC在温度为 52 5℃、应变速率为 2 .0 8× 1 0 - 1 s- 1 时最大延伸率可达 2 2 8% ,应变速率敏感性指数为 0 .39。超塑性拉伸断口上存在丝棒状物质     

High strain rate superplasticity of SiC whisker reinforced pure aluminum composites

１　ＩＮＴＲＯＤＵＣＴＩＯＮＳｏｍｅｆｉｎｅｃｅｒａｍｉｃｗｈｉｓｋｅｒｏｒｐａｒｔｉｃｌｅｒｅｉｎｆｏｒｃｅｄａｌｕｍｉｎｕｍｍａｔｒｉｘｃｏｍｐｏｓｉｔｅｓｃａｎｅｘｈｉｂｉｔａｔｏｔａｌｅｌｏｎｇａｔｉｏｎｏｆ２００％～６００％ａｔａｈｉｇｈｓｔｒａｉｎｒａｔｅ（＞１０－２ｓ－１）［１～８］．Ｔｈｅｈｉｇｈｓｔｒａｉｎｒａｔｅｓｕｐｅｒｐｌａｓｔｉｃｉｔｙ（ＨＳＲＳ）ｉｓｖｅｒｙａｔｔｒａｃｔｉｖｅｆｏｒｃｏｍｍｅｒｃｉａｌａｐｐｌｉｃａｔｉｏｎｓｂｅｃａｕｓｅｏｎｅｏｆｔｈｅｍａｊ…     

High strain rate superplasticity at intermediate temperatures of the Al 7075 alloy severely processed by equal channel angular pressing

The mechanical properties of an overaged Al 7075-O alloy processed by ECAP were examined by tensile tests at intermediate-high temperatures ranging from 250 to 400 °C and strain rates from 10⁻⁵ to 10⁻¹ s⁻¹. The influence of the number of ECAP passes on the ductility enhancement was evaluated. Elongation to failure, e_F, significantly increased with increasing the number of ECAP passes up to 8 at 130 °C. The alloy processed under these conditions exhibited a maximum value of 322% at 300 °C and an initial strain rate of 10⁻³ s⁻¹. High strain rate, e_F = 210%, at a strain rate as high as 10⁻² s⁻¹. The large elongations together with lower stresses and lower stress exponents than those for the start material confirm that grain boundary sliding (GBS) is the operative deformation mechanism. A loss of superplastic behaviour at temperatures above 350 °C is related to abnormal grain growth and a change of deformation mechanism.     

Advances and applications in high strain rate superplasticity

High strain rate superplasticity (i.e., superplastic behavior at strain rates over 10^-2 s^-l) has been observed in many metallic materials such as aluminum alloys and their matrix composites and it is associated with an ultra-fine grained structure of less than about 3 pm. Its deformation mechanism appears to be different from that in conventional superplastic materials. A new model was considered from the viewpoint of the accommodation mechanism by an accommodation helper such as a liquid or glassy phase. The new mechanism was proposed in which superplasticity was critically controlled by the accommodation helper both to relax the stress concentration resulting from the sliding at grain boundaries and/or interfaces and to limit the build up of internal cavitation and subsequent failure. The possibility of the industrial applications was demonstrated for high-strain-rate superplasticity.     

含钪铝合金的钎焊工艺

探讨了Al-Zn-Mg-Sc-Zr铝合金采用炉中钎焊的可行性。结果表明，通过选用合理的钎料和钎剂组合以及优化试验条件下的钎焊工艺参数，可获得焊缝表面成形良好的钎焊接头。对获得的接头进行力学性能测试，结果表明，文中试验条件下获得的钎焊接头具有相对较高的抗剪强度；金相组织观察显示，钎缝金属组织致密，未发现有气孔、夹渣和微裂纹等焊接缺陷；扫描电镜观察显示接头拉伸断口大部呈韧性断裂机制。钎缝微区成分分析表明钎料与母材之间存在明显的合金元素互扩散，钎缝与母材之间结合良好；X射线衍射相结构分析表明，接头钎缝金属中含有Al，Sc、Al，Zb等组成相，对提高接头抗翦强度具有重要作用。     

原位生成Al3Zr/6063Al复合材料的高应变速率超塑性

采用熔体直接反应法,原位制备5%wtAl3Zr/6063Al复合材料。在450℃进行70%变形量锻造预处理,然后进行搅拌摩擦大塑性加工,通过XRD、SEM、EDS、超景深及TEM等分析测试方法研究其高应变速率超塑性。结果表明,通过锻造和搅拌摩擦加工处理后,复合材料的平均晶粒尺寸小于10μm。在350℃~500℃,初始应变速率为1.0×10-3s-1~1.0×10-1s-1范围内,复合材料都表现出超塑性。在500℃,初始应变速率为1.0×10-2s-1,延伸率达到最大值330%,反应敏感指数m值为0.45。分析超塑性变形的主要机制是动态连续再结晶与晶界、位错滑移共同协调完成。     

含钪7xxx系铝合金的再结晶

采用金相显微镜和透射电子显微镜研究了含钪Al-Zn-Mg-Cu-Zr系铝合金组织的再结晶,测试了不同温度下退火1h合金的硬度。结果表明:含0.20%Sc的7xxx系铝合金(冷变形量50%)的再结晶起始温度为475℃,再结晶终了温度为525℃。合金在均匀化以及热加工过程中析出细小、弥散的二次A l3(Sc,Zr)粒子钉扎位错、亚晶界和晶界,使回复过程中的位错运动受阻,保持基体内较高的位错的密度,阻碍加热时位错重新排列呈亚晶界以及更进一步发展成大角度晶界的过程;阻碍了再结晶核心长大过程,阻碍大角度晶界的迁移,从而提高再结晶温度。     

Processing commercial aluminum alloys for high strain rate superplasticity

The superplastic forming of sheets, although used on a small, specialized scale, has not yet been adapted for high-volume purposes. In processing for superplastic properties, the key microstructural features are grain size and grain-boundary misorientation. Current research trends are two-fold: to evaluate bulk processing of ultrafine-grained materials, and to understand the superplastic behavior of ultrafine-grained materials. Work is continuing on understanding the relationship between grain size and superplastic strain rate and superplastic temperatures. In this paper, strategies are reviewed for producing microstructures with enhanced superplastic characteristics. For more information, contact R.S. Mishra, University of Missouri, Department of Metallurgical Engineering, Rolla, Missouri 65409, (573) 341-6361: e-mail rsmishra@umr.edu.     

Microstructures and mechanical properties of Al-Mg and Al-Zn-Mg based alloys containing minor scandium and zirconium

1　INTRODUCTIONAddingofminorMn ,Cr ,Ti,B ,Zr ,Sc ,Agintoaluminumalloyscanremarkablychangethemi crostructuresandpropertiesofaluminumalloys[18] .Amongthem ,theeffectofminorScandZrhasre ceivedspecialattention .Onthe 1stInternationalScandiumConferenceheldinMoscowin 1994 ,Rus sianmetallurgistsdescribedtheapplicationprospectofaluminumalloyscontainingScinaerospace ,aviation ,warshipsandnuclearindustry ,whichhasstimulatedmanyindustrialcountries’researchinterestinthiskindofalloys .Atpresent…     

Using ECAP to achieve grain refinement, precipitate fragmentation and high strain rate superplasticity in a spray-cast aluminum alloy

An aluminum 7034 alloy, produced by spray casting and with an initial grain size of ˜2.1 μm, was processed by equal-channel angular pressing (ECAP) at 473 K to produce an ultrafine grain size of ˜0.3 μm. It is shown that the rod-like MgZn₂ precipitates present in the as-received alloy are broken into very small spherical particles during ECAP and these particles become distributed reasonably uniformly throughout the material. The presence of these fine MgZn₂ particles, combined with a distribution of fine Al₃Zr precipitates, is very effective in restricting grain growth so that submicrometer grains are retained at elevated temperatures up to at least ˜670 K. Tensile testing of the pressed material revealed high elongations to failure, including elongations of >1000% when testing at a temperature of 673 K at initial strain rates at and above 10⁻² s⁻¹. These results confirm the occurrence of high strain rate superplasticity in the spray-cast alloy.     

含钪Al-Cu-Li-Zr合金热压缩变形流变应力行为

在变形温度为653K~773 K,应变速率为0.001s-1~10s-1的条件下,采用Gleeble——1500热模拟试验机对含钪Al-Cu-Li-Zr合金的热变形行为进行了研究。结果表明:含钪Al-Cu-Li-Zr合金流变应力随变形温度升高和应变速率的降低而减小;变形初期,应力值随应变的增加迅速提高,显示出明显的加工硬化效应。当应力值达到峰值后,随着变形增加,流变应力逐步降低,合金出现明显的软化现象。根据流变应力本构方程及利用作图法和线性回归方法求解得出各参数数值,得出流变峰值应力方程,利用此方程预测的流变峰值应力与实验结果吻合得较好。     

Study on high strain rate superplasticity of A 6061Al alloy composite reinforced with 30 Vol.% AlN particulate

An investigation on the superplastic behavior of 30 vol.% AlNp/6061Al composite prepared by powder metallurgy (PM) techniques was carried out. Superplastic tensile tests of the composite were performed at strain rates ranging from 10° to 10⁻³ s⁻¹ and at temperatures from 823 to 893 K. A fine-grained structure prior to superplastic testing was obtained by hot rolling after extrusion. The highest total elongation to failure of 438% was achieved at a temperature of 863 K and at an initial strain rate of 1.67×10⁻¹ s⁻¹ and the highest value of the strain rate sensitivity index (m) was 0.42 for the composite. Differential thermal analysis (DTA) was used to investigate the possibility of any partial melting in the vicinity of optimum superplastic temperatures. The formation of a liquid phase is attributed to the melting of the Al-Si eutectic phase at the surface of the AlN particulates at elevated temperatures, as determined by electron probe microanalysis (EPMA). The influence of the microstructure and the fracture behavior on the superplastic behavior of the composite was studied by transmission electronic microscopy (TEM) and scanning electron microscopy (SEM). A large number of matrix filaments were present at the fracture surfaces of the specimens when superplastic deformation of the composite was performed under the optimum superplastic test conditions. The presence of dislocations and fine recrystallized grains in the test specimens suggested that they play an important role in the high-strain-rate superplasticity for this composite.