Effect of multi-step slow shot speed on microstructure of vacuum die cast AZ91D magnesium alloy

Two multi-step （two-step and three-step） slow shot speeds were used in the vacuum die casting process of AZ91D magnesium alloy. The vacuum pressure variation in the die cavity before mold filling was monitored by using a pressure sensor. The microstructures of the produced castings were analyzed with optical microscope and image analysis software. The experimental results demonstrate that, the vacuum pressure in the die cavity at the beginning of mold filling is significantly reduced by using three-step slow shot speed, resulting in a low gas porosity level in the produced castings. At an appropriate multi-step slow shot speed, the dwell time of the liquid metal in the shot sleeve before mold filling can be reduced and the flow of the liquid metal in the shot sleeve at the later stage of the slow shot process can be restrained, which cause a low externally solidified crystal content in the produced castings.

Design and Verification of an Auxiliary System for High Vacuum Die Casting

Vacuum die casting is the optimal method to produce high quality aluminum alloy components.At present,there are still very few systematic studies on vacuum die casting theory and equipment design.On the basis of the existing theories of the vacuum die casting pumping and venting systems,a simplified model is established in this research.The model has an aggregate unit consisted of ＂vacuum pump ＋ buffer tank＂ and a cylindrical container（including the shot sleeve,cavity and exhaust channel）.The theoretical analysis is carried out between the cavity pressure and the pumping time under different volume models.An auxiliary system for high vacuum die casting is designed based on the above analysis.This system is composed of a vacuum control machine and a new vacuum stop valve.The machine has a human-computer control mode with ＂programmable logic controller（PLC） ＋ touch screen＂ and a real-time monitoring function of vacuum degree for buffer tank and die cavity.The vacuum stop valve with the ＂compressed gas ＋ piston rod ＋ labyrinth groove＂ structure can realize the function of whole-process vacuum venting.The new system shows great advantages on vacuuming the cavity with a much faster speed by making tests on an existing die casting mold and a 250 t die casting machine.A die cavity pressure less than 10 kPa can be reached within 0.8 s in the experiment and the porosity of castings can be greatly decreased.The systematic studies on vacuum die casting theory and equipment have a great guiding significance for high vacuum die casting,and can also be applied to other high vacuum forming in related theoretical and practical research.

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.

Synergistic effects of composition and heat treatment on microstructure and properties of vacuum die cast Al-Si-Mg-Mn alloys

The purpose of this study was to prepare high-quality Al-Si-Mg-Mn alloy with a good combination of strength and ductility employing the vacuum-assisted high-pressure die cast process. An orthogonal study of heat treatments was conducted to design an optimized T6 heat treatment process for both Al-10%Si-0.3%Mg-Mn and Al-11%Si-0.6%Mg-Mn alloys. The results demonstrate that no obvious blisters and warpage were observed in these two alloys with solid solution treatment. After the optimal T6 heat treatment of 530°C×3 h + 165°C×6 h, Al-11%Si-0.6%Mg-Mn alloy has better mechanical properties, of which tensile strength, yield strength and elongation reached 377.3 MPa, 307.8 MPa and 9%, respectively. The improvement of mechanical properties can be attributed to the high density of needle-like β″(Mg_5Si_6) precipitation after aging treatment and the fine and spherical eutectic Si particles uniformly distributed in the α-Al matrix.

Vacuum assisted high-pressure die casting of AZ91D magnesium alloy at different slow shot speeds

The effects of vacuum assistance on the microstructure and mechanical properties of high-pressure die cast AZ91 D alloy at different slow shot speeds were evaluated. Plate-shaped castings of AZ91 D alloy were carried out on a TOYO BD-350V5 cold chamber die casting machine incorporated with a self-improved TOYO vacuum system. It was found that the vacuum pressure in the die cavity at the beginning of mold filling increases with the increase of slow shot speed, following a cubic polynomial curve, resulting in a decline in the porosity-reduction ability of vacuum assistance with the increase of slow shot speed. The externally solidified crystal（ESC） contents in conventional and vacuum die castings behave similar against the slow shot speed. The tensile properties of vacuum die castings were strongly influenced by the ESC content at relative low slow shot speeds. With the increase of slow shot speed, the influence of the gas porosity level in vacuum die castings would get prominent.

Characterization of A390 aluminum alloy produced at different slow shot speeds using vacuum assisted high pressure die casting

The effects of vacuum assistance on the microstructure and mechanical properties of high pressure die cast A390alloy at different slow shot speeds were evaluated.Plate-shaped specimens of hypereutectic A390aluminum alloy were produced on a TOYO BD?350V5cold chamber die casting machine incorporated with a self-improved TOYO vacuum system.According to the results,the vacuum pressure inside the die cavity increased linearly with the increasing slow shot speed at the beginning of mold filling.Meanwhile,tensile properties of vacuum die castings were deteriorated by the porosity content.In addition,the average primary silicon size decreased from23to14μm when the slow shot speed increased from0.05to0.2m/s,which has a binary functional relationship with the slow shot speed.After heat treatment,microstructural morphologies revealed that needle-shaped and thin-flaked eutectic silicon particles became rounded while Al2Cu dissolved intoα(Al)matrix.Furthermore,the fractography revealed that the fracture mechanism has evolved from brittle transgranular fracture to a fracture mode with many dimples after heat treatment.

Effect of vacuum on porosity and mechanical properties of high-pressure die-cast pure copper

Pure copper tensile bars were produced by conventional die casting(HPDC) and vacuum-assist die casting(VADC) processes. Porosity and mechanical properties were investigated by using optical microscopy(OM), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), X-ray computed tomography(XCT) and tensile tester. Results show that porosities including gas porosity and shrinkage porosity could be observed in copper castings. Since the application of vacuum could reduce filling related gas entrapment and facilitate solidification due to the increased heat transfer between metal and die, both number and size of the entrapped gases, as well as shrinkage porosities were significantly reduced in vacuum-assist die castings of pure copper. The porosity fraction decreased from 2.243% to 0.875% compared with that of the conventional die casting. Besides, mechanical properties were improved significantly, i.e., by 15% for ultimate tensile strength and three times for elongation.

Effect of Injection Velocity on Structure Part Characteristic in A50 Die Casting Process with High Vacuum System

When diecasting large and thin Mg alloy parts,material defects occur,which include porosity,nonuniform mechanical properties,irregular surfaces,and incomplete filling.To resolve these problems,it is necessary to have uniform injection velocities and temperatures as well as control the melt.This study investigated the feasibility of producing large and thin components using a die caster by attaching a high vacuum system.In particular,the effects of injection velocity on surface quality and the mechanical properties of the products were investigated.Hence,an injection velocity scheme and a die structure capable of casting in a vacuum were proposed.As a result,it was found that the critical low injection velocity was 0.2 m/s to produce large thin Mg alloy structures having good mechanical properties.

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(VL),high shot speed(VH),pouring temperature(Tp)and initial die temperature(Tm),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 Tp from680to720℃or the VL from0.1to0.4m/s.In addition,the influence of the VH and Tm on IHTC could be negligible.

一体压铸用免热处理铝合金自主研发及应用

为获得性能优异的一体压铸用免热处理铝合金,通过调整合金中各元素的质量分数,设计出3种不同成分比例的Al-Si系免热处理铝合金,采用差示扫描量热仪(DSC)、金相显微镜、扫描电镜、拉伸试验机和电磁共振式疲劳试验机对3种合金的熔化温度区间、组织相构成、断口形貌、拉伸与疲劳性能进行分析,结果表明,2#合金的熔化温度区间为55℃,抗拉强度、屈服强度、断后伸长率分别为303 MPa、153 MPa、11.3%,在1×10^(7)循环周次下的轴向拉压疲劳强度均值为125 MPa,因此,2#合金具有良好的铸造流动性、金相组织、强韧综合性能与铸造工艺性,且疲劳性能优于汽车行业普遍应用的AlSi9Cu3(Fe)压铸合金。

High-tenacity in-situ Ti/Zr-based bulk metallic glasses composites fabricated by industrial high-pressure die casting

The glass-forming ability and mechanical properties of metallic glasses and their composites are well known to be sensitive to the preparation conditions and are highly deteriorated by industrial preparing conditions such as low-purity raw materials and low vacuum.Here,we showed that a series of in-situ bulk metallic glass composites(BMGCs)which exhibit excellent ductility and segmental work hardening were successfully developed utilizing a high vacuum high-pressure die casting(HV-HPDC)technology along with industrial-grade raw materials.The tensile properties of these BMGCs are systematically investigated and correlated with the alloy microstructure.As compared with the copper mold suction casting method,the volume fraction difference of the dendrite phase for the BMGCs with the same composition is not significant when fabricated by the HV-HPDC,whereas the size of theβ-phase is generally larger.Insitu BMGCs with the composition of Ti_(48)Zr_(20)(V_(12/17)Cu_(5/17))19 Be 13 obtained by the HV-HPDC process show ductility up to 11.3%under tension at room temperature and exhibit a certain amount of work hardening.Two conditions need to be met to enable the BMGCs,which are prepared by vacuum die-casting to retain favorable ductility:(1)The volume fraction ofβphase stays below 62%±2%;(2)The equiaxed crystals with a more uniform size in the range of 5-10μm.Meanwhile,the results of the present study provided guidance for developing BMGCs with good ductile properties under industrial conditions.

Cu含量和热处理工艺对Al-Si-Mg-Mn-xCu铸造铝合金显微组织和力学性能的影响

采用三维X射线显微镜、光学显微镜、扫描电子显微镜、透射电子显微镜及硬度测试系统研究Cu含量及热处理工艺对真空压铸Al-Si-Mg-Mn-xCu合金显微组织和力学性能的影响。研究发现,虽然Cu含量增加会提高铸锭中气孔的密度和尺寸,但是Cu添加将促进凝固过程中含Cu初生相(Q-Al_(5)Cu_(2)Mg_(8)Si_(6)和θ-Al_(2)Cu)的形成,从而提高合金性能。合金中形成5种不同结构的初生相,包括共晶Si、α-Al(Fe,Mn)Si、β-Mg_(2)Si、Q-Al_(5)Cu_(2)Mg_(8)Si_(6)和θ-Al_(2)Cu相。随着Cu含量增加,θ相的面积分数迅速增加,α-Al(Fe,Mn)Si相面积分数首先降低,随后缓慢增加,而Q相的变化趋势与α-Al(Fe,Mn)Si相相反。这些初生相在热处理过程中会出现不同的演变规律。在随后的时效处理过程中,Q'和θ'相的协同析出能显著提高合金的时效硬化潜力。

基于真空压铸技术的机壳压铸模设计

通过对机壳压铸件的结构工艺分析,介绍了真空压铸技术下模具的浇注系统、成型零件、侧向分型与抽芯机构、推出机构、溢流与排气系统、温度控制系统等机构的设计要点,相比普通压铸的模具,能有效减低压铸原材料的损耗,提升压铸件质量,为类似模具的设计提供一定的参考借鉴。

新能源汽车底盘副车架一体化压铸技术研发与应用

新能源汽车底盘副车架尺寸大,结构复杂,力学性能要求高,常规一体化压铸工艺无法满足设计要求。采用三级抽真空技术,提高了模具型腔的真空度,真空度达到≤15 kPa;采用集群局部挤压技术,改善了区域组织结构,有效缩减了缩孔,减少了气孔。生产实践证明,两种技术的应用使压铸件的力学性能达到了设计要求,提升了压铸件品质,提高了生产效率,产品合格率达到95%以上。

深冷、固溶和时效处理对真空压铸铝合金摩擦磨损性能的影响

为提升真空压铸铝合金的力学性能及耐磨性,借助场发射扫描电镜和电子万能拉伸试验机等技术,系统研究了深冷+低温短时固溶+低温时效的处理工艺对真空压铸铝合金微观组织和摩擦磨损性能的影响.结果表明:经过深冷+低温固溶时效处理后,合金的组织结构相更加均匀,共晶Si相圆整度明显提高,长针状的Al_(5)FeSi相棱角钝化,大大降低了对铝基体的割裂作用.此时,合金的硬度提高至124.6 HV,抗拉强度提升至249.5 MPa,伸长率提高至7.72%.深冷+低温固溶时效态合金的摩擦磨损性能得到显著提高,在不同的载荷下,深冷固溶时效态试样的犁沟最浅,剥落区相对最少,表现出更优异的耐磨性能.

热处理对高真空压铸AlSi10MnMg合金拉伸性能的影响

分别对高真空压铸AlSi10MnMg合金进行T5(180℃×2 h)、T6(515℃×1 h空冷+175℃×2 h)和T7(460℃×1 h水冷+175℃×2.5 h)热处理,研究了不同热处理条件下该合金的显微组织和拉伸性能。结果表明:经过T5热处理后的铸态试验合金铝基体相长大,圆整度较高,晶粒尺寸主要集中在20~80μm,硅相仍呈细长状,与铸态试验合金相比,试验合金的抗拉强度提高了8.9%,断后伸长率降低了9.1%;经过T6和T7热处理后,铝基体相形状不规则程度降低,晶粒尺寸分别为2~50,2~30μm,组织更均匀致密,硅相由铸态时的细长状演变为规则的圆形,试验合金的抗拉强度分别降低了26.0%和23.9%,断后伸长率分别提高了54.5%和72.7%;铸态和T5态试验合金的拉伸断裂方式均为韧脆混合断裂,T6和T7态试验合金的断裂方式则以韧性断裂为主,其中T7态试验合金拉伸断口中的韧窝细密且深,塑性更好。

工艺参数对6082-T6/AlSi10MnMg异种铝合金热融自攻丝接头成形性的影响

为探究工艺参数对6082-T6/AlSi10MnMg真空压铸铝合金热融自攻丝接头成形性的影响,采用正交试验法,将穿孔转速、进给速度和拧紧扭矩作为试验变量,通过极差分析研究了工艺参数对最小衬套高度和平均螺牙深度的影响规律。在正交试验结果的基础上,建立了参数值与被测指标的响应面模型,研究了各参数对成形质量影响的显著性。对最优工艺参数组合的接头进行了强度测试。结果表明,穿孔转速和进给速度对最小衬套高度影响显著,但二者的交互作用对最小衬套高度影响较小。平均螺牙深度主要受拧紧扭矩的影响,穿孔转速和进给速度对平均螺牙深度的影响较弱。在拉拔和拉剪工况下,工艺参数对接头强度有较大影响,参数优化后接头强度分别提高了9.48%和8.64%,剪切工况下接头强度变化较小。

新能源汽车一体化压铸微量喷涂温度调控实验研究

一体化真空压铸是当前实现新能源汽车轻量化的主流技术,随着压铸技术的不断成熟,一体化结构件尺寸逐渐增大,对模具温度的精准控制提出了更高的要求,微量喷涂对模具温度的合理调控直接决定了压铸件的质量和生产效率。本文建立了微量喷涂模具温度调控系统方案,构建了微量喷涂模具温度控制系统实验平台,通过实验和仿真分析了喷涂距离、喷嘴相对位置、喷涂流量等因素对微量喷涂冷却效果的影响。实验结果验证了模具温度在线检测和温度控制系统的可靠性和实用性,为提升铸件质量和延长模具使用寿命提供了有效的技术支持。

车身真空高压压铸技术研究

铝合金真空高压压铸技术在汽车行业逐步得到应用,研究分析了真空高压压铸材料、工艺、产品及现阶段重点问题。概括了热处理和免热处理材料的物理特点、化学成分及机械性能;介绍了真空高压压铸工艺流程和产线、工艺设计、工艺参数、成形性能;分析了产品性能、厚度、尺寸、连接、维修、模具寿命现阶段的主要问题;总结了真空高压压铸技术的优势并展望其发展前景。

乘用车车身大型压铸件设计与研究

为实现乘用车车身大型压铸件设计,从压铸工艺种类和特点出发,分析了高真空压铸在乘用车车身大型压铸件中的应用,并针对关键接头、重要梁系、主要加强件、减振器塔座、A柱模块、后地板总成、前舱总成等常见压铸件应用部位,从壁厚、加强筋和顶针布局方面分析了压铸件的设计原则和要求。