Two methods of electromagnetic continuous casting(EMCC) and normal continuous casting were carried out aiming at improving the formability of AZ31 magnesium alloy .The macrostructure,microstructure,formability and component segregation of both billets were compared and the fracture mechanism of magnesium alloy was analyzed by fractography of magnesium alloy sample.The result showed that the EMC alloy crystal was much finer and more uniform than normal cast billet,and its dendrites crystal was fragmentized,full equiaxed grains came forth.Mechanical properties of EMCC cast(plasticity especially) was enhanced prominently than normal casting billets,its tensile and yield strength and elongation increased by 17%,50% and 81% than normal billet,respectively.The break appearance had a toughness break character and the element segregation was decreased by 73% for Zn and 67% for Mn,respectively.

The macrostructure and solute distribution in the cross-section of ingot of magnesium alloy AZ31 by electromagnetically continuous casting (EMC) were studied. The result shows that the size of crystal grain obtained by EMC in suitable technique can be refined. Adopting the casting velocity with 8 cm/min and the apparent direct current with 40 A, magnesium alloy AZ31 round billet (phi 162 mm) has uniform and equiaxed macrostructure. The macro-segregation in the billet is improved greatly. The average segregation of elements Zn and Mn have been reduced by 73% and 67% respectively.

The effects of electromagnetic continuous casting on the phase constituent, microstructure and corrosion resistance of magnesium alloy AZ31 were investigated. The results reveal that although the change of phase constituent in electromagnetic continuous casting AZ31 magnesium alloy can not be observed, the grain size in the billet is refined with broken dendrites and uniform continuous β-Mg17 Al12 phase distributed around bulk α-Mg phase. Compared with that of the billets in conventional continuous casting, the corrosion rate of AZ31 magnesium alloy billets in electromagnetic continuous casting is decreased by 29.4 % in 5% NaCl salt spray testing, which is attributed to the continuously distributed net β-Mg17 Al12 phase effectively controlling the corrosion of Mg alloy.

A test of electromagnetically continuous casting(EMC) was used to cast AZ31 alloy to study the effect of electromagnetic field on the billets,in which the solidification structure and mechanical properties of the billets cast with or without electromagnetic field were examined.The result shows that the optimum distribution of magnetic induction intensity is obtained at the apparent direct current of 40?50 A,and the grain size obtained by EMC is fine and uniform,the dendritic crystal are fragmentated.The mechanical properties of the billet casted by EMC are improved obviously compared with those casted by the traditional casting,and the tensile strength,yield strength and elongation are increased by about 17%,50% and 81%,respectively.AZ31 magnesium alloy casted by EMC usually shows flexible fracture.

中国汽车工业的快速发展为铝合金压铸行业提供了重要的发展契机.参考了大量国内外压铸企业,对铝合金压铸车间的合金熔化、压铸生产、铸件清理、质量控制及车间环境等工艺及车间布局进行分析.认为合理的工艺布局应从产品和生产纲领出发,结合国情和本地区的特点,做到经济、高效,满足可持续发展的需要.

合理地选择合金是进行压铸产品设计的重要环节之一.本文基于模糊综合评判原理,建立了压铸镁合金材料选择系统,快捷有效地选择出最合适的合金牌号.同时,以一MP3外壳选材为例,具体说明系统运行过程.

结合生产情况,对感应电炉熔炼条件下的A380铝合金精炼工艺进行了工业试验和探讨.研究认为,由于产生新的夹杂,氮气精炼效果并不理想,并造成炉壁清渣困难.熔剂精炼效果较好,炉壁清渣容易,但其可操作性差.在对熔炼过程中合金及溶渣的运动情况进行分析的基础上指出,溶渣容易在坩埚侧壁和侧壁与底部的交界沉积.建议采用氩气吹熔剂的精炼方法解决精炼问题,并对炉壁渣的清理方法提出了建议.

Mg-9Al-xRE magnesium alloys were studied, where x is 0, 0.4, 0.8, 1.2 and 1.6% (in weight percent, wt%), respectively. Influence of rare earths (RE) on microstructure and strength in both T4 (solute heat treatment) and T6 (solute heat treatment and artificial ageing treatment) were investigated. Strength of specimen was tested at ambient temperature. The microstructure was analyzed by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction analysis. RE additions improved T4 tensile strength of the treated alloys. Small addition (0.4wt%) of RE greatly improved the strength of ageing treated (T6) Mg-9Al alloy, but further additions caused decreasing.

Based on the characteristics of magnesium alloys, testing methods for research on hot-tearing were experimentally investigated and analyzed. Temperature,linear shrinkage and shrinkage power during solidification of magnesium alloys were measured with a testing system for hot-tearing behavior. The phase precipitated under the commercial casting solidification condition was analyzed with a thermo-analysis system. These methods can provide important experimental support to understanding the hot-tearing mechanism of magnesium alloys. Hot-tearing susceptibility of magnesium alloys can be efficiently evaluated with crack-ring method. However,the same-length test bar method (permanent mold or sand mold) was not suitable for testing of magnesium alloys.

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.

Hot-tearing susceptibility of Mg–9Al–xZn alloys is studied. Crack-ring molds were used to test the hot-tearing susceptibility. In situ thermal analysis, optical microscopy, scanning electron microscopy (SEM) and line scan were used to examine the hot-tearing behavior. Hot-tearing originates along the grains at the end of solidification. With Zn additions, the quantity of phase with low melting point in grain boundaries is increased, its melting point is decreased and the hot-tearing susceptibility is increased. The segregation of Zn element in grain boundaries is the main contribution to the high hot-tearing susceptibility of Mg–9Al–xZn alloys.

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.

A new method of investigating the hot tearing behavior of magnesium alloys is developed. The results of measurement, by EDAX and optical microcopy revealed that the end-solidifying temperature was around the eutectic temperature under practical solidification conditions, because of a quantity of eutectic caused by dendritic segregation. The temperature at which hot tearing occurred most probably in the AZ91 alloy was the practical end-solidifying temperature, which was 424.2 °C in the present solidification conditions. The appearance of eutectic was the inducement for hot tearing of AZ91 alloy.

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 method to investigate the hot cracking behavior of alloys is introduced. With the accurate record of the stress and temperature data during the alloy's solidification as well as the metallography, the hot cracking behavior of AZ91 magnesium alloy is studied. It is concluded that, the temperature at which the hot cracking occurs mostly is the actual end-solidifying temperature (424.2 degreesC) under the current experimental conditions. The appearance of eutectic at the end of solidification is the direct reason induced hot cracking in AZ91 magnesium alloy.

设计了一种新的合金热裂行为测试系统. 该系统通过数/模转换, 用微机对凝固过程中的温度、应力和收缩信号数据进行采集和进一步的处理, 并描绘其曲线. 实验结果表明, 在正常凝固条件下, AZ91合金并不按平衡相图凝固, 而是有共晶相析出; 在合金凝固后期, 存在一"冲击”收缩, 是"冲击”收缩导致了合金凝固过程热裂的产生.

Based on the mechanical parts assembly of the twin bar tester of hot tearing- linear contraction for alloy, a new way to testing hot tearing behavior of Mg alloy was developed. In the system, resin precoated sand was used as molding material to solve the combustion of Mg alloy during pouring process. The signal data of temperature, stress and shrinkage were recorded and further treated with curves drawn by computer through A/D conversion. Results indicated that AZ91 alloy would precipitate eutectic phase not coinciding with equilibrium phase diagram under the conventional solidification condition. The temperature most susceptible to be hot torn was located near the practical solidified-end temperature(420 ℃) for AZ91 alloy.

对热裂形成理论和热裂倾向性评定方法进行了总结分析.重点介绍了强度理论、晶间搭桥理论、凝固收缩补偿理论和CSC判据、HCS判据.并对热裂今后的研究提出了看法.