ZK60-RE alloys were made by melting ZK60 alloy and cerium rich rare earth ( RE) in a crucible electric furnace. The content of RE was 0, 0.5, 1, 1.5, 2, and 3 wt-%, respectively. The influence of RE on the microstructure and tensile mechanical properties of ZK60 magnesium alloys was studied. The results showed that cerium rich misch metal ( MM) had an obvious effect of reducing the grain size of the as extruded ZK60 alloys. The ultimate and yield strengths of extruded ZK60 alloys were improved by the addition of RE. The ultimate and yield strength increased with increasing RE content in the range investigated. It was also found that the ultimate strength and yield strength decreased with increasing extrusion temperature. The improvement in tensile properties of ZK60-RE alloys was due to the extrusion texture and the fine microstructure induced by RE additions.

综述了镁合金的几种塑性变形机制,并介绍了ZK60合金在不同温度下的变形机制.同时综述了镁合金的动态再结晶机制,以及动态再结晶对变形和超塑性变形的作用.

In situ composites of Zn–27Al–6.3Mg–3.7Si alloy have been fabricated by centrifugal casting using the heated permanent mold. This kind of composites is consisted of three layers: inner layer segregates lots of blocky primary Mg2Si and a little blocky primary Si, middle layer does not contain primary Mg2Si and primary Si, outer layer contains a little primary Mg2Si and primary Si. The position, quantity and distribution of primary Mg2Si and primary Si are determined by solidification velocity under the effect of centrifugal force and their floating velocity inward. The inner and outer layer contained primary Mg2Si and primary Si exhibit much higher hardness and wear resistance than the middle layer.

ZK60–RE alloys were made by melting ZK60 alloy and cerium-rich rare earth (RE) metal in an electric furnace. The content of RE is 0, 0.5, 1, 1.5, 2, 3 wt.% RE, respectively. The influence of RE on microstructure and tensile mechanical properties of ZK60 magnesium alloys was studied. The results showed that cerium-rich misch metal (MM) had an obvious effect of reducing the grain size of the as-extruded ZK60 alloys. The ultimate and yield strengths of extruded ZK60–RE alloys were improved by the addition of RE. The ultimate and yield strength increased with increasing RE content in the range investigated. It is also found that the ultimate strength and yield strength decrease with increasing extrusion temperature. The improvement of tensile properties of ZK60–RE alloys was due to the extrusion texture and the fine microstructure induced by RE additions.

In-situ composite of Zn-27Al-6.3Mg-3.7Si alloy was fabricated by centrifugal casting using the heated permanent mold. This kind of composite is consisted of three layers, inner layer segregates lots of blocky primary Mg_2Si and a little blocky primary Si, middle layer contains no primary Mg_2Si and primary Si, outer layer contains a little. Zn-27Al-6.3Mg-3.7Si alloy solidifies according to following steps: firstly, the precipitation of primary Si and primary Mg_2Si, secondly, the precipitation of Zn-phase enriched by Al, thirdly, the precipitation of Mg-Zn compound, and lastly, the occurrence of ternary or quaternary eutectic reaction. The position, quantity and distribution of primary Mg_2Si and primary Si are determined by solidification velocity under the effect of centrifugal force and their floating velocity inward. The inner and outer layer contained primary Mg_2Si and primary Si exhibit much higher hardness and wear resistance than the middle layer.

Various wrought magnesium alloys and their workability are reviewed. High-temperature worka-bility,heat treatment and grain refinement of wrought magnesium alloys are discussed. Future development directions and application areas for wrought magnesium alloys are also introduced.

运用金相显微镜、电子探针和X-ray等手段分析了AZ61合金添加稀土元素Ce后铸态显微结构的变化.结果表明,Ce的加入细化了β相和晶粒,并减少了β相的量.Ce在AZ61合金中以呈块状和杆状Al4Ce化合物的形式存在,这两种化合物熔点极高,几乎不溶于基体,有极少部分偏聚在晶界上.固溶处理后,AZ61合金中的β(Mg12Al17)相几乎全部溶入基体;而加入稀土Ce后,AZ61合金中的Al4Ce化合物几乎很少溶入基体.Ce的加入能够提高AZ61合金基体相的显微硬度,但幅度不大;而将其固溶处理后,Ce显著提高了AZ61合金的显微硬度.

Effects of Zn and RE additions on the solidification behavior of Mg–9Al alloy were studied. Zinc (Zn) and rare earths (RE) elements were added to a maximum quantity of 1.2 and 1.6wt.%, respectively. Cooling curves were obtained under commercial production conditions. Hot tearing susceptibility was investigated using crack-ring molds. Microstructure was analyzed by metallographic examination and electron probe micro-analysis. Zinc additions decreased the end-solidifying temperature, promoted the precipitation of Mg17Al12 in grain boundaries and increased the hot-tearing susceptibility coefficient (HSC). Al4RE phase precipitation slowed down the temperature decrease at the initial stage of solidification. RE additions had little effect on HSC of Mg–9Al with low or no Zn content, while when Zn content was exceeded 0.8 wt.%, RE additions decreased HSC of Mg–9Al alloys distinctly.

研究了Zn元素对Mg-9Al合金的凝固行为,尤其是对热裂倾向性的影响.通过热分析手段考察合金的凝固特征.用热裂环法评价合金的热裂倾向性,引入了热裂倾向性(HSC)因子的概念.并通过金相观察、扫描电镜和电子探针对合金的凝固、热裂行为进行了研究.研究发现,在凝固过程中Zn,Al元素由于晶间偏析而在晶界富集.Zn元素的加入,增加了晶界低熔点相的量,并降低了其熔点,从而明显增加了合金的热裂倾向性.Mg-9Al-xZn合金的热裂产生于凝固后期,呈沿晶断裂.加入Zn元素对Mg-9Al合金的晶粒有细化作用.

Models for solidification of Mg-9Al alloy were developed on the basis of thermodynamics. with temperature descending, the nucleation of crystals and their growth proceed continuously all through the range of solidification. Solid fraction, volume shrinkage and segregation in Mg-9Al alloy were studied mathematically during the solidification of casting. The results indicate that solidification ended at about the eutectic temperature, instead of solidus, the change of volume during solidification is non-linear, i.e. quick at initial stage, steady when the remaining liquid having eutectic composition, and seriously shrinkages at the end caused by eutectic transformation. Experimental measurement agrees well with the simulation results.

Superplastic behavior of a commercial AZ31 magnesium alloy is investigated at temperatures ranging from 623 to 723 K and strain rates ranging from 10 -5 to 10 -3?s -1. The results showed that the alloy exhibits excellent superplasticity, and the maximum elongation-to-failure reaches 314%. The alloy also shows a high strain rate sensitivity exponent of 0.4. Microstructural observations suggest that grain boundary sliding (GBS) makes a substantial contribution to the superplastic deformation, and the dynamic recrystallization is the accommodated mechanism for the deformation.

利用等离子发射光谱仪、差分扫描量热仪(DSC) 、电镜以及金相分析等手段, 研究了RE对消失模铸造B319铝合金组织的影响. 结果表明, 在消失模铸造条件下,0.15%RE可使B319铝合金的硅相得到较好的变质效果. 但当RE＞0.2%时, 会出现富稀土的粗大块状金属间化合物La3Al8Si2, 而对机械性能产生不利影响. 当Fe/Mn=1.2时, 消失模铸造组织中存在中国文字状的α-Fe和针状β-Fe铁相以及Al2Cu相. Al2Cu相可以离异共晶的形式析出, β-Fe及Si相均可以作为Al2Cu相的形核基底. 而在金属型铸造组织中, 铁相则完全以针状的β-Fe形式存在. 研究还表明, 0.02%Sr变质使B319合金共晶转变温度下降了7 ℃. 而RE的加入会使合金的共晶温度升高, 采用0.2%RE对B319合金进行变质处理, 其共晶温度从570.0 ℃升高到了572.0 ℃.

A new in-situ Zn-Al-Si surface composites was fabricated by using centrifugal casting. A high-volume fraction of primary Si particles in the inner layer was achieved. The formation mechanism of the gradient was discussed. The effect of technological parameters on the composites was investigated. Testing results show that the hardness and wear resistance of the composites depend mainly on the distribution of the primary silicon particles along radial direction. The inner layer of the composite shows the highest hardness and best wear properties. The fracture mode of the composites is primarily brittle. The inner layer of the composite exhibits more deformation than the inner layer during the fracture.

The damping capacity of MgLi4Al and MgLi8Al alloys was studied. The results showed that the damping capacity of Mg-Li-Al alloys increases with the temperature and lithium content. For MgLi8Al alloy as an example, the damping capacity go up to Q-1= 0.01, in the range of high damping metallic materials. The higher damping capacity of MgLi8Al alloy may be attributed to the interface damping between α(Mg) and β(Li) phases.

The study on interfacial structure and tensile properties of MgLi matrix composites. The results showed that there was a clear interface between the MgLi matrix and SiC whiskers. Calculation of thermodynamics confirmed that the clear interface between the matrix and SiC whiskers may contribute to the low reactionary potential or the low reactionary dynamics. However, some SiC whiskers were attacked, As a result, SiC whiskers connected with matrix in {111} and formed 70.5 degrees or 109.5 degrees stages on the whiskers surface in {111} face. The reason was the lower interfacial energy of {111} face. Tensile test confirmed that the SiCw/MgLiAl composites showed higher tensile strength and higher modulus compared with MgLi matrix. Moreover, the specific strength and specific modulus were also increased obviously.

研究了不同锂含量的Mg Li Al合金的力学性能和阻尼性能。结果表明 ,随锂含量的增加 ,Mg Li Al合金的密度和抗拉强度降低、塑性明显提高 ;而Mg Li Al合金的阻尼性能随锂含量的增多和温度的提高而明显增高 ,其中Mg 8Li 1Al合金的室温延伸率为 35% ,室温阻尼性能高达 0 .0 1。Mg 8Li 1Al合金的阻尼明显大于Mg 4Li 1Al合金的阻尼 ,是由于Mg 8Li 1Al合金具有α +β双相共晶混合组织 ,α和β相的相界面在循环载荷下产生微滑移 ,而形成相界阻尼 ;而Mg 4Li 1Al合金中只存在α单相组织。