不同慢压射速度条件下AZ91D镁合金的真空辅助压铸

对不同慢压射速度条件下真空辅助对AZ91D镁合金压铸件组织及力学性能的影响进行了评估。在联合有自行改进的TOYO真空系统的TOYO BD-350V5型冷室压铸机上制备片状AZ91D镁合金压铸件。研究发现,充型时型腔真空压力随着慢压射速度的升高呈现3次方增长,导致真空辅助对压铸件中气孔的降低能力随着慢压射速度的降低而下降。常规和真空压铸件中压室预结晶组织（ESC）含量随着慢压射速度的变化趋势相似。在较低慢压射速度时,真空压铸件拉伸性能受ESC含量的影响很大,随着慢压射速度的升高,真空压铸件中气孔含量的影响将变得显著。     

Effect of different processing parameters on interfacial heat-transfer behavior in high-pressure die-casting process

Vacuum die casting can reduce the “air entrapment” phenomenon during casting process. Based on the temperature measurements at metal–die interface with different processing parameters, such as slow shot speed (V_L), high shot speed (V_H), pouring temperature (T_p) and initial die temperature (T_m), inverse method was developed to determine the interfacial heat transfer coefficient (IHTC). The results indicate that a closer contact between the casting and die could be achieved when the vacuum system is used. It is found that the vacuum could strongly increase the values of IHTC and decrease the grain size in castings. The IHTC could have a higher peak value with increasing the T_p from 680 to 720 °C or the V_L from 0.1 to 0.4 m/s. In addition, the influence of the V_H and T_m on IHTC could be negligible.     

压铸A380合金力学性能及热处理工艺性能研究

以A380压铸铝合金为研究对象,设计了压铸工艺参数,并对压铸件进行了热处理试验。通过密度测定、力学性能测试和金相观察,分析了压铸工艺参数对铸件性能的影响规律,探求了热处理对压铸件性能的影响。研究表明:压力增加,铸件的密度和强度增加;压力一定时,低速速度对铸件力学性能的影响大于高速速度;压铸工艺改进可进一步提高材料的性能,抗拉强度接近365 MPa,伸长率可达4.2%;合理的固溶+低温时效处理后,材料具有更高的综合力学性能,屈服强度达205 MPa,抗拉强度394 MPa,伸长率可达7.8%。     

Comparison of mechanical properties of die cast aluminium alloys: cold v. hot chamber die casting and high v. low speed filling die casting

Abstract

In this paper, the mechanical properties of die cast aluminium alloys made by various die casting technologies were examined. To create high quality aluminium alloy die castings, two die casting processing technologies were employed. These were (a) ultra slow speed filling cold chamber die casting and (b) high speed hot chamber die casting. Significant improvements of the fatigue and mechanical properties were obtained for both die casting systems compared to the normal high speed cold chamber die casting technique. By comparing ultra slow die casting with hot chamber die casting, it was found that the fatigue and mechanical strengths from hot chamber die casting were higher than those for ultra slow filling die casting. The differences in material strength were attributed directly to the material properties, e.g. microstructural morphology and internal defects. Spherical fine dendritic cells in the hot chamber die casting sample gave rise to high fatigue crack growth resistance; the low crack growth resistance for cold chamber die cast aluminium is mostly due to the growth of aluminium rich α phase and the presence of eutectic silicon fibres. The fatigue strength was also related to the number of internal defects, e.g. the lower the defect rate on the fracture surface, the higher the fatigue resistance and mechanical strength. The characteristics of the principal internal defect were different depending on the die casting technology: this showed fine porosity for hot chamber die casting but solidification shrinkage and the scattered chill structure for slow and high speed cold chamber die castings. The reasons for the change of material strength were therefore influenced by the die casting process.     

压射速度和料饼厚度对压铸AM60B镁合金压室预结晶的影响(英文)

采用不同的慢压射速度、快压射速度和不同的料饼厚度,压铸直径6.4mm、标距长度50mm的标准拉伸试样,观察压铸试样的显微组织,分析不同工艺对压室预结晶的影响,讨论压室预结晶与工艺参数的关系。结果表明:随着料饼厚度的增加,组织中的压室预结晶数量减少;低的慢压射速度可获得较大尺寸的压室预结晶;高的快压射速度有利于形成球状的压室预结晶。     

压铸工艺参数对ADC12Z压铸件孔洞和抗拉强度的影响

研究了铸造压力、料柄厚度、低速速度和高速速度对ADC12Z压铸件孔洞和抗拉强度的影响。结果表明:铸造压力和料柄厚度对密度、孔洞面积分数、孔洞平均尺寸及抗拉强度的影响较低速速度和高速速度显著。随着铸造压力和料柄厚度增大,压铸件孔洞面积分数和孔洞平均尺寸减小,密度和抗拉强度增大。     

Mechanical properties of thixomolded AZ91D magnesium alloy

Tensile properties of thixomolded AZ91D alloy were studied to investigate the fracture mechanism by the microstructure and decohesion surfaces of tensile specimens which were manufactured at different processing conditions including barrel temperature, shot velocity, mold temperature and screw rotation speed. The results revealed that mechanical properties of thixomolded AZ91D mainly depended on porosity level, the size and volume fraction of primary solid phase and the size of α-Mg and β-Mg₁₇Al₁₂ in liquid phase. The increase in barrel temperature and shot velocity would cause the increase of both strength and ductility, while increasing mold temperature or improving screw rotation speed was coupled by the reduction of tensile properties. The tensile behaviors for different processing parameters were reasonably interpreted through the dependant factors during the deformation.     

Effect of arc re-melting on microstructure,mechanical and tribological properties of commercial 390A alloy

To investigate the effect of the arc re-melting on the microstructure, mechanical and tribological properties of the 390A alloy, its ingot produced by the conventional induction melting method was subjected to the arc re-melting process. The microstructure of the 390A alloy was examined by OM and SEM. Mechanical properties of the 390A alloy were determined by the Brinell method and tensile tests. Tribological properties were investigated with a ball-on-disc type tester. It was observed that the microstructure of both conventional induction melted and arc re-melted 390A alloys consisted of α(Al), eutectic Al–12Si, primary silicon particles, θ-CuAl₂, β-Al₅FeSi, δ-Al₄FeSi₂, and α-Al₁₅(FeMnCu)₃Si₂ phases. Re-melting with the arc process caused grain refinement in these phases. In addition, after this process, the α(Al) phase and primary silicon particles were dispersed more uniformly, and sharp edges of primary silicon particles became round. The arc re-melting process resulted in an increase in the hardness of the 390A alloy produced by the conventional method from 102 HB to 118 HB and the tensile strength from 130 to 240 MPa. It also caused an increase in the wear resistance of the 390A alloy and a decrease in the friction coefficient.     

A study of metal/die interfacial heat transfer behavior of vacuum die cast pure copper

High pressure die casting copper is used to produce rotors for induction motors to improve efficiency. Experiments were carried out for a special "step-shape" casting with different step thicknesses. Based on the measured temperature inside the die, the interfacial heat transfer coefficient(IHTC) at the metal/die interface during vacuum die casting was evaluated by solving the inverse problem. The IHTC peak value was 4.5×10~3-11×10~3 W·m~(-2)·K~(-1) under the basic operation condition. The influences of casting pressure, fast shot speed, pouring temperature and initial die surface temperature on the IHTC peak values were investigated. Results show that a greater casting pressure and faster shot speed could only increase the IHTC peak values at the location close to the ingate. An increase of pouring temperature and/or initial die surface temperature significantly increases the IHTC peak values.     

铝合金半固态压铸工艺参数及性能研究

应用具有不同厚度的简单板材模具来系统研究压铸工艺参数对A356铝合金半固态压铸件性能的影响,以优化半固态压铸工艺及其参数.试验结果表明,对A356铝合金半固态压铸,其性能随压射压力的增大而提高,当压射压力大于100 MPa,则性能基本上不再提高.压铸速度过小或过大会降低压铸件的性能.另外建压时间、坯料加热温度、模具预热温度以及脱模剂等参数对半固态压铸件性能也有明显的影响.     

S390粉末高速钢真空气淬的显微组织及性能

研究了不同淬火温度、不同冷却方式对S390粉末高速钢进行真空热处理的显微组织及性能的影响。试验结果表明,经不同工艺淬火后,S390粉末高速钢的晶粒度在13级左右,其中的合金碳化物数量减少、尺寸变小,硬度均大于63.2 HRC。经真空气淬后的S390粉末高速钢试样中均可得到下贝氏体组织,且在下贝氏体片状组织中及残留合金碳化物周围有纳米椭圆(球)状合金碳化物析出。     

热处理工艺对高真空压铸Mg–8Gd–3Y–0.4Zr镁合金组织及力学性能的影响

研究T4和T6热处理状态下高真空压铸Mg-8Gd-3Y-0.4Zr（质量分数,%）合金的微观组织、化合物含量、力学性能及断裂行为。铸态Mg-8Gd-3Y-0.4Zr合金微观组织主要由α-Mg和共晶Mg24（Gd,Y）5化合物组成。经固溶处理后,共晶化合物大量溶解于镁基体,合金主要含过饱和α-Mg及方块相。固溶合金中方块相的含量随固溶温度的升高而增大,力学性能也有所提高。根据微观组织结果,确定475℃,2 h为Mg-8Gd-3Y-0.4Zr合金最优固溶方案。合金的最佳屈服强度为222.1 MPa,延伸率可达15.4%。铸态,T4状态下和T6状态下合金的拉伸断裂模式为穿晶准解理断裂。     

AM6OB镁合金压铸工艺的研究

研究了压射比压、浇注温度、模具温度、压射速度四个压铸参数对AM60B镁合金显微组织、铸造性能和力学性能的影响,探明了其在冷室压铸备件下的最佳工艺,简单分析了压铸态组织,并成功的实现了镁合金灯罩铸件的试制。     

高强韧Mo-0.1Zr合金的制备、性能及组织

采用球磨制备Mo-0.1Zr粉末,经压制成型、预烧、高温烧结和真空热处理后,制备抗拉强度超过650 MPa、伸长率大于30%的高强韧Mo-0.1Zr合金,研究真空热处理对合金性能与显微组织的影响。结果表明:经高温烧结后,Mo-0.1Zr合金与纯Mo相比性能提高不明显,断口形貌呈明显的沿晶脆性断裂特征;但经真空热处理后,Mo-0.1Zr合金的性能显著提高,抗拉强度提高了40%、伸长率从7.3%提高到31.2%,合金断口也由沿晶脆性断裂转变为穿晶韧性断裂,且部分晶粒呈韧性撕裂特征。真空热处理温度对合金性能的影响很大,真空热处理温度过高容易使晶粒长大,导致性能提高程度下降;而真空热处理温度过低难以起到消除晶体缺陷的作用,对合金性能提高有限。     

Effect of DH treatment on microstructure and mechanical properties of an LM28–0.3wt.% Nd hypereutectic aluminum silicon alloy

In this article, a novel heat treatment method, deformation heat (DH) treatment (extrusion aging), was employed on a hypereutectic aluminum silicon alloy (LM28-0.3wt.%Nd), and its effect on microstructure and mechanical properties of this alloy was investigated. It can be concluded that the eutectic microstructure disappears after the DH treatment, in the meantime the morphology of α(Al) solid solution was transformed from fir-tree and cellular to equiaxed, Si was refined with grain sizes of about 1-10 μm and distributed dispersedly, even some of them became globular shape, which can reduce stress accumulation effectively. Mechanical properties test indicated that the DH treatment could significantly improve the room-temperature strength and have little effect on the high-temperature strength of LM28-0.3wt.%Nd alloy. The fracture mechanism is ductile fracture by fracture morphology analysis.     

喷丸直径对GH4169合金性能和损伤演化的影响

采用半自动光学显微镜、激光共焦显微镜、MTS-Landmark电液伺服力学性能试验机等设备,研究了GH4169合金经不同直径弹丸喷丸处理后的微观组织和力学性能。利用数字图像相关方法(DIC),对材料单轴拉伸过程的表观损伤演化行为进行分析。结果表明,随着弹丸直径由ϕ0.6 mm增大到ϕ4.3 mm,GH4169合金的表面细晶层厚度由420 μm 增大到530 μm,其表面粗糙度最大较原始试样增大了80.8%。喷丸处理后,材料的屈服强度和抗拉强度均有所提高,其伸长率下降。随着塑性变形增加,喷丸前后GH4169合金的损伤演化规律相似,变形初期材料发生均匀变形且变形缓慢,损伤因子达到临界值后材料开始快速损伤。喷丸直径越大,临界塑性应变越小,材料越早发生快速损伤。建立了不同喷丸直径GH4169合金的损伤演化方程,对喷丸强化材料的寿命评估具有重要意义。     

Si含量和热处理制度对铸造Al-Si合金组织和性能的影响

为提高铸造Al-Si合金的力学性能,研究了Si含量和热处理制度对Al-Si合金组织和性能的影响。结果表明,Si含量、固溶冷却介质、固溶温度、时效时间、时效温度对Al-Si合金硬度的影响依次减小。Al-Si合金的最优Si含量及热处理制度为Si含量12%,480 ℃固溶120 min,盐溶液冷却及175 ℃时效90 min。随着Si含量的增加,Al-Si合金硬度和抗拉强度提升;但当Si含量超过共晶点时,方块状初生硅相析出,易形成应力集中使得合金强度降低,断裂方式由韧性断裂变为解理断裂。铸态Al-Si合金中共晶硅为长针状,经最优工艺热处理后,长针状转变为短棒或颗粒状,共晶硅更加分散,在拉伸过程中应力集中减少,位错运动阻力增加,使得Al-Si 合金的力学性能提高。     

Effect of Admixtures of Iron and Silicon on the Structure and Cracking of Near-Edge Volumes in Rolling of Large Flat Ingots from Alloy 7075

The effect of the content of iron and silicon admixtures in aluminum alloy 7075 on the composition, morphology, and fineness of phase components in the microstructure of ingots with cross section of 390 – 1330 mm in homogenized condition is studied. The mechanical properties of ingots at room and enhanced temperatures are determined depending on the content of iron and silicon in the alloy. The effect of the iron and silicon content in alloy 7075 on fracture of near-edge volumes in the process of hot rolling of plates with a thickness of 76.3 – 152 mm is determined.__________Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 35 – 39, January, 2005.     

正确选择慢压射速度

卧室冷室压铸机压铸时,压室底部被浇入的金属熔体所覆盖,熔体上部分至压室顶部的空间被气体所占据.在慢压射时(即三级压射系统的第一级压射或四级压射系统的第二级压射),这些气体,在慢压射参数正确时,通过模具排出,否则会卷入金属熔体一同充填型腔,成为铸件内气孔的主要形成原因,由此弄清慢压射行程中冲头速度与金属熔体波的形貌,可正确选择慢压射速度.     

基于CAE的铝合金标准试样的压铸工艺方案优化

压铸工艺方案的合理性对标准压铸试样的力学性能具有重要影响。采用Flow-3D软件对现有推荐的标准试样压铸工艺方案进行了模拟分析和优化;同时设计和优化了适于高真空压铸的工艺方案。结果表明,现有的压铸工艺方案在低速充填阶段时,试样内浇道附近的横浇道中会出现金属液回流卷气现象。将直浇道与横浇道的过渡圆角加大到30mm时,该回流卷气现象明显减小。改用锥形横浇道并辅以缓冲包结构时,回流和卷气部位则移至两端的缓冲包附近,可避免卷气的金属液进入试样型腔中,有利于铸件品质的改善。采用在试样溢流槽侧面设置排气道时,能有效消除不同试样间排气道的封闭现象,从而保证后充填试样有足够的排气时间,有利于铸件内部品质的提高。