Opportunities and challenges of Chinese die-casting market

The present status and perspectives of Chinese die-casting market were commented. In 2003, the total output of die castings in the whole country was 708000 tons, in which the outputs of Al-alloy, Zn-alloy, Mg-alloy, Cu-alloy die castings were 474600 tons, 222000 tons, 5800 tons, 5600 tons, respectively, each accounted for 67％, 31.35％, 0.85％, 0.8％ of the total. The annual sale volume of die-casting machines was approximately 1800. And the gross output value of dies approached RMB 38 billion, in which die-casting dies accounted for about 10％. In the die-casting industry of the entire country, the foreign capital enterprises, public-run enterprises, township and village enterprises, private enterprises accounted for over 80％ of the total die-casting enterprises. Super huge die-casting groups are forming.     

AM60B镁合金压铸模浇注系统的模拟与优化

设计出2种类型的镁合金压铸浇口及浇注系统,运用模拟软件对2种浇注系统进行模拟,分析液态金属充型及凝固过程中流场和温度场的分布。根据凝固规律有效预测铸件中可能存在的缩孔及气孔缺陷的分布,优化浇注系统结构。结果表明:在浇注温度690℃、模具初始温度200℃、冲头压射速度3m/s条件下,压铸件质量较好。     

Creep mechanism of as-cast Mg-6Al-6Nd alloy

The creep mechanism of as-cast Mg-6Al-6Nd alloy was studied. The stress exponent for creep is 5.8 under the applied stresses of 50–70 MPa at 175°C. The activation energy for creep is 189 kJ·mol⁻¹ under the applied stress of 70 MPa in the range of 150–200°C. The true stress exponent and threshold stress for creep are calculated as 4.96 and 10.2 MPa, respectively. The true stress exponent indicates that its creep mechanism belongs to the dislocation climb-controlled creep, which is in agreement with the microstructure changes before and after creep. The high value for stress exponent is attributed to the interaction of Al₁₁Nd₃ phase with dislocations. The activation energy is more than the self-diffusion activation energy of Mg, which is attributed to the load transfer taking place from the matrix to Al₁₁Nd₃ phase during creep.     

Effects of electric parameters on microstructure and properties of MAO coating fabricated on ZK60 Mg alloy in dual electrolyte

Micro-arc oxidation (MAO) process was carried out in a dual electrolyte system of NaAlO2 and Na3PO4 on ZK60 Mg alloys to explore the effect of electric parameters including current density, frequency, duty cycle and oxidation time on the evolution of coatings and other characteristics. The microstructural characteristics of coatings were observed by scanning electron microscopy (SEM) combined with the analysis of voltage-time responses during MAO process. Test of weight loss was conducted at a 3. 5％ NaCl solution to assess the resistance to corrosion. The results indicate that the current density and duty cycle play key roles on the coating quality. The peak voltage during MAO process increased with the increase in current density but the coating would be more easily detached when the current density was beyond a critical value. Voltage during MAO and microstructure of the coating were affected remarkably by duty cycle, and corrosion resistance was improved greatly when duty cycle was 40％. By means of single variable experiments, MAO process with optimized electric parameters was developed, which corresponds to the current density of 20 A·dm-2, frequency of 500 Hz, duty cycle of 40％ and oxidation time of 15 min.     

Effect of Ca addition on the as-cast microstructure and creep properties of Mg-5Zn-5Sn magnesium alloy

The effect of Ca addition on the as-cast microstructure and creep properties of Mg-5Zn-5Sn magnesium alloy was investigated. The results indicate that adding 1.0 wt.% Ca to Mg-5Zn-5Sn alloy can effectively refine the as-cast microstructure of the alloy, and the CaMgSn phase with high thermal stability is formed in the alloy. In addition, adding 1.0 wt.% Ca to Mg-5Zn-5Sn alloy can also improve the creep properties of the alloy. After adding 1.0 wt.% Ca to Mg-5Zn-5Sn alloy, the second creep rate of the alloy at 150°C and 50 MPa for 100 h decreases from 4.67 × 10⁻⁸ to 1.43 × 10⁻⁸ s⁻¹. The strengthening mechanism is mainly attributed to the microstructural refinement and the formation of CaMgSn phase.     

热处理对浇铸和压铸AZ91D-RE镁合金组织与性能的影响

分别采用金属模浇铸和压铸方法制备了相同成分的AZ91D-RE合金,应用金相显微镜、X射线衍射仪、扫描电镜和硬度计分析和测试了热处理对合金组织和性能的影响,并对其耐腐蚀性能进行了探讨.结果表明,铸态下AZ91D-RE压铸合金组织由α-Mg和Mg17Al12相组成,而浇注合金中还出现了MgY相;经固溶处理后,压铸合金中的Mg17Al12相全部消失,而浇注合金中尚有部分Mg17Al12相未溶解;随着时效时间的延长,压铸镁合金的硬度先升高后下降,并在11 h达到最大值,而浇注镁合金的的硬度一直升高,表现为时效未完成;在相同条件下,压铸AZ91D-RE合金的组织比浇铸合金的细小,并且,压铸AZ91D-RE合金的耐腐蚀性能也均优于浇铸合金的.     

不同时效态7050铝合金时效成形中析出相对应力松弛行为的影响

采用设计的应力松弛试验研究了不同时效态(固溶态,欠时效态和峰时效态)7050铝合金内析出相对时效成形过程中应力松弛行为的影响,并通过位错热激活动力学参数计算和显微组织表征分析析出相与位错运动的交互作用.结果 表明,时效成形过程中析出相对位错热激活运动有明显的阻碍作用,因此含有不同尺度析出相铝合金的应力松弛行为表现不同,...     

AM60压铸镁合金表面ZrO_2微弧氧化陶瓷层的制备方法研究

为了改善镁合金的微弧氧化膜层的性能,利用两步法在AM60压铸镁合金表面制备了ZrO_2微弧氧化膜层.研究了膜层在恒电压控制方式下的生长规律,测量了膜层在w(NaCl)=3.5%溶液中的极化曲线,分析了膜层的物相组成.结果表明:在400 V恒压微弧氧化处理时,微弧氧化膜层的平均生长速度最高可达3.5 μm/min:试样在w(NaCl)=3.5%溶液中的极化曲线显示,镁合金经过两步法在锆盐溶液中微弧氧化后,其腐蚀电位正移,腐蚀电流降低,腐蚀速度大幅降低,其耐蚀性得到了大幅度提高.两步法制备微弧氧化膜层主要由ZrO_2、ZrP_2、Mg_3(PO_4)_2、MgF_2相组成,在溶液中添加的Zr元素可以通过微弧氧化处理时的复杂反应进入膜层中,膜层表现出的优异耐蚀性主要源于膜层中存在ZrO_2陶瓷.     

Effect of Ca addition on microstructure and impression creep behavior of cast AZ61 magnesium alloy

Microstructure and creep properties of AZ61 alloy containing 1 and 3 wt.% Ca were investigated. The creep properties were examined using impression method under different stresses between 200 and 500 MPa at the temperature ranging from 423 to 491 K. The microstructure of AZ61 alloy contains α(Mg) matrix and Mg₁₇Al₁₂ intermetallic phases. It is shown that adding Ca to AZ61 alloy reduces the amount of Mg₁₇Al₁₂ phase via forming (Mg, Al)₂Ca phase; furthermore, increasing the Ca content to 3 wt.% leads to the formation of (Mg, Al)₂Ca phase, as well as the elimination of the Mg₁₇Al₁₂ phase. Creep properties of AZ61 alloy are improved with the Ca addition. The improvement in creep properties is attributed to the reduction in the amount of Mg₁₇Al₁₂ phase and the formation of (Mg, Al)₂Ca phase with high thermal stability. According to the obtained creep data, it is concluded that the pipe diffusion−climb controlled dislocation creep is the dominant creep mechanism and Ca addition has no influence on this mechanism. The effect of pre-deformation on the creep properties of AZ61+3%Ca alloy reveals that the creep resistance of the alloy depends on the continuity of (Mg, Al)₂Ca phase. It is decreased by reducing the phase continuity.     

压铸模镶块的热疲劳失效行为

对工作1200模次发生热疲劳失效的压铸模镶块进行失效机理分析,同时建立了压铸过程的热-力耦合数值分析模型,研究了镶块在压铸服役过程中温度场和应力场的演变规律,并对其寿命进行预测。结果表明,镶块的失效是由于压铸过程中受到高温铝熔液的冲刷和冷却液的急冷引起的热疲劳行为所致;在循环压铸过程中,镶块凸台转角处出现应力集中,最大等效应力约为788 MPa,热疲劳裂纹在该处萌生和扩展;采用低周疲劳寿命预测模型对镶块热疲劳寿命进行预测,镶块热疲劳寿命约为1651次,与镶块实际热疲劳寿命非常吻合,这表明本文建立的热-力耦合数值模型可为压铸模镶块的可靠性设计提供借鉴。     

铝合金流变成形标准试样的压铸模设计

根据铝合金半固态浆料的充型特点，为防止出现卷气、夹杂和充型不完整等常见缺陷，设计了一套铝合金流变成形标准试样的压铸模具。用该模具成形的试样可用于铝合金流变成形工艺、组织与性能的研究。     

AZ80镁合金的高温拉伸变形行为

采用拉伸至断裂实验,在温度为300、350、400和450℃,应变率分别为10~（-2）和10~（-3）S~（-1）条件下,研究AZ80镁合金的拉伸行为。并采用变化应变率拉伸实验在5×10弓至2×10~（-2）S~（-1）的应变率范围内进行变形机制研究。结果表明：该材料在400和450℃下具有超过100％的高伸长率,其应力指数为4．29,变形激活能为149．60kJ／mol。初始细晶粒在均匀变形区的高温变形中较为稳定,其变形机制为晶界滑移和位错攀移蠕变的竞争机制。基于该机制所建立的数学模型的模拟结果与实验数据吻合。     

锌合金喷头盖压铸模设计

对带有圆弧孔及外螺纹特征的锌合金喷头盖进行了模具设计,模具采用齿轮齿条抽芯机构实现铸件圆弧抽芯,稳定性好,精度较高;采用外链条及齿轮传动机构实现铸件螺纹抽芯,安全可靠,保证了铸件质量及尺寸精度,可供类似铸件的模具设计参考。     

铝-硅合金砂型铸件改为压铸生产的工艺改进

通过一个铝-硅合金端盖压铸件设计实例,探讨了铝-硅合金砂型铸件改为压铸生产时,要在合金化学成分、熔炼工艺和铸件的工艺性能等方面,根据压铸工艺的特点对铸件整个生产工艺进行改进,以满足压铸生产的特殊要求。压铸铝-硅合金中ω（Fe）可以达到1．0％。ω（Fe）〈0．150%时,ω（Mn）要达到0．5％-0．8％,以防止粘模。对于不太重要的铝合金压铸件可以省略熔炼过程中的变质处理过程,通过合理设置加强筋、减少壁厚、减小拔模斜度等措施,改善压铸件的结构工艺性。     

Effect of rare-earth element Sm on the corrosion behavior of Mg-6Al-1.2Y-0.9Nd alloy

The effect of Sm (0 wt.%-2 wt.%) addition on the corrosion behavior of Mg-6Al-1.2Y-0.9Nd alloy in 3.5 wt.% NaCl solution has been studied by static corrosion tests, corrosion morphology observation, corrosion scale and microstructure analysis. The results show that, with the increasing of Sm content, the corrosion rate of the alloy decreases at first, then increases and reaches the valley at 0.5 wt.% Sm. The reason is that the proper content of Sm addition can refine the precipitates and make the component and microstructure uniform, and therefore, it remarkably improves the corrosion resistance of the alloy.     

熔体热速处理对铸造Mg合金组织和力学性能的影响

研究了熔体过热和热速处理对AZ91铸造Mg Al Zn合金组织和力学性能的影响。在含有Mn和钢坩埚内壁未刷有涂料的前提下 ,熔体温度 (82 0℃ )不够高时 ,会引起晶粒的粗化 ;熔体温度 (870℃ )足够高时 ,镁合金结晶晶核的增加引起了基体组织的细化 ,同时组织中的γ强化相比未高温过热时弥散、均匀 ;热速处理后组织部分保留了高温过热时的特性 ,从而使镁合金的力学性能和铸件质量得到提高。     

ZL112Y铝合金半固态压铸过程微观组织的演变

研究了ZL112Y压铸铝合金在半固态压铸成形过程中的组织演变过程。观察了原始料坯、半固态重熔后快速水淬的料坯、压铸机压室内的冲头料坯以及压铸模内的内浇口和半固态压铸零件中不同部位的固相a组织的形貌，同时采用定量金相的方法分析了这些部位的固相α组织的圆形度、粒子平均直径和单位面积粒子个数等参数。结果表明：半固态重熔过程使原始料坯中的α枝晶组织变成节杆状和球团状组织，转变的原因是枝晶熔断机制；重熔后料坯在压室内的运动过程使半固态料坯中的α粒子尺寸的不均匀性得以消除，同时使残留的枝晶得以进一步的分离细化；α相均匀化和细化了的半固态浆料进入铸型后液相更容易到达铸件远端，液相和固相充型是2个不同的过程，液相的充型速率要大于固相。     

Al—2Mg合金的动态再结晶

单相Ａｌ２ Ｍｇ 合金在３００ ～５３０ ℃ 以０ ．０６９ ～１ ．５８７ｓ－ １ 形变速率扭转到真应变５ ．５ ， 随后立即水冷。采用真应力－ 真应变曲线， 偏振光金相和透射电子显微镜研究该合金热扭转过程的动态复原机制。试验证实， 该合金热扭转过程中发生了动态再结晶， 但在一定的Ｚ 参数范围内发生， Ｚ 参数过大或过小， 只发生动态回复。显微组织分析并没有发现层错的存在。发生动态再结晶的原因是动态回复被抑制， 即在较高形变温度下， 加大形变速率， 而在较低形变温度下， 降低形变速率。     

Effect of Ni on Mg based hydrogen storage alloy Mg3Nd

Magnesium-neodymium based alloys were prepared by induction melting in an alumina crucible under protection of pure argon atmosphere. XRD patterns show that the as-melted Mg-Nd and Mg3NdNi 0.1 diffraction peaks can be excellently indexed with D03 structure (BiF3 type, space group Fm3m ). The lattice constant of Mg3Nd phase is 0.7390 nm, which is determined by XRD analysis using Cohen's extrapolation method. The reversible hydrogen storage capacity reaches 1.95wt.% for Mg3Nd and 2.68wt.% for Mg3NdNi0.1 . The desorption of hydrogen takes place at 291 ℃ for Mg3Nd and at 250 ℃ for Mg3NdNi 0.1 . The alloys could absorb hydrogen at room temperature with rapid hydriding and dehydriding kinetics after only one cycle. The enthalpy (ΔH ) and entropy (ΔS ) of Mg3Nd-H dehydriding reaction were -68.2 kJ·mol-1 H2 and -0.121 kJ·(K·mol)-1 H2 determined by using van't Hoff plot according to the pressure-composition-isotherms (P-C-I) curve measured at different temperatures. Hydrogen absorption kinetic property of Mg3NdNi 0.1 alloy was also measured at room temperature.     

Effect of rare earth additions on microstructure and mechanical properties of AZ91 magnesium alloys

In order to meet the demands of high temperature components in automobile, the microstructure and mechanical properties of several new die-casting AZ91-rare earth (RE) magnesium alloys were studied. The alloys were characterized by optical microscopy (OM), scan electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), tensile and creep tests. The results show that Ce addition has little effect on the mechanical properties of AZ91 alloy at high temperature, while Y and Nd addition play important role in the improvement of creep resistance. New alloys containing Y or Nd with excellent high temperature performance are selected to produce cylinder head cover of high power diesel engine of Red Flag car and oil pan of Besturn car. The new magnesium alloys with RE addition for die-casting have potential to produce power-train parts, and can greatly decrease weight.