高压电气产品铝合金支架铸件的工艺优化

高压电气铝合金支架铸件,原工艺采用金属型树脂砂芯倾转铸造一模一件,由于产品需求量激增,质量要求逐渐提高,现有的一模一件倾转模具已满足不了客户需求。通过优化工艺方案,采用金属型低压铸造(取消树脂砂芯)一模八件的生产方式,大大提高了铸件的生产效率和工艺出品率,并降低了成本。     

钛对7050铸轧板材裂纹调控的影响

本文采用场发射高分辨扫描电子显微镜,差示扫描量热仪,X射线衍射仪等先进设备研究了微量Ti元素对7050铝合金铸轧薄板裂纹形成的影响规律和调控机理,结果表明：微量的Ti可以显著细化铸轧板的晶粒组织,改变晶粒生长方式,改善合金的流动性,使铸轧组织更加致密,消除合金内局部应力集中,抑制铸轧裂纹出现。而且,适量Ti元素还可以缩短铸轧7050铝合金的固液相线区间,减小晶核凝固前沿温度梯度,有效抑制成分偏析,从而降低晶界低熔点化合物数量,减少粗大第二相的产生,从而大幅增强铸轧铝合金的抗热裂能力。当7050铸轧板中Ti含量达到0.2%时,Ti对铸轧板裂纹的抑制作用最佳,而过量的Ti元素会聚集形成大块的含Ti脆性相,反而破坏组织的致密性,促进裂纹的萌生。     

Integrated bottom up and top down approach to optimization of the extrusion process

Boal BV and the University of Twente participate in research projects focused on improvement of die design methods for aluminum extrusion dies. Within this research empirical knowledge is combined with insights gained from numerical process simulations. Design rules for improvements to the geometry and functionality of flat and porthole dies have been defined. For porthole dies this has led to enhanced die stability and significant reduction of scrap. For both flat and porthole dies an increase in production speed and a reduction of wear has been obtained. This paper will describe the scope of this research and present results achieved in industrial practice.     

The effect of die casting machine parameters on porosity of aluminium die castings

The primary objective of this research is to investigate the effect of machine related parameters on porosity formation in the aluminum die casting process. The amount and distribution of porosity in die castings was examined in relation to plunger velocity during the 1st phase, fast shot set point, plunger velocity during the 2nd phase, die cavity filling time and multiplied pressure during the 3rd phase.

Standard statistical analysis was performed in order to identify the effect of each of the considered parameters and parameter interactions on porosity formation. It was found that, among the parameters considered, multiplied pressure, plunger velocity in the 2nd phase and die cavity filling time have the most significant effect on porosity formation. Using optimal die casting machine parameter levels, the optimum porosity value of aluminum alloy die-castings was predicted. The results were confirmed by further experiments.     

Improving die casting processes through optimization of lubrication

Lubrication plays a significant role among the processes that affect aesthetic quality in die casting. Nevertheless, comprehensive investigations are still missing in literature. In this paper, the effect of lubrication is investigated and optimized, by focusing on its influence on the die temperature. Indeed, since the surface quality of castings is related to the interaction between melt and die, lubrication allows ejection of castings without generating defects and cooling of the die, by preserving its surface. Hence, the die temperature should be accurately selected and spraying should be improved to achieve the optimal temperature. In the experimentation proposed, the lubricant release agent percentage and the lubrication duration have been varied to trade-off between some conflicting effects, while making the die temperature approach the ‘Nukiyama point’. At the same time, reduction of the cycle time has been obtained. The results corroborate the approach, since defects are reduced after optimization.     

Feasibility of semi-solid die casting of ADC12 aluminum alloy

The feasibility of semi-solid die casting of ADC12 aluminum alloy was studied. The effects of plunger speed, gate thickness, and solid fraction of the slurry on the defects were determined. The defects investigated are gas and shrinkage porosity. In the experiments, semi-solid slurry was prepared by the gas-induced semi-solid (GISS) technique. Then, the slurry was transferred to the shot sleeve and injected into the die. The die and shot sleeve temperatures were kept at 180 °C and 250 °C, respectively. The results show that the samples produced by the GISS die casting give little porosity, no blister and uniform microstructure. From all the results, it can be concluded that the GISS process is feasible to apply in the ADC12 aluminum die casting process. In addition, the GISS process can give improved properties such as decreased porosity and increased microstructure uniformity.     

大型铝合金模锻件内部缺陷的模拟分析

针以吕合金件的锻造过程。采用实验与计算机模拟相结合的办法，分别对锻件内部冶金缺陷的变化及其应变场进行了分析。研究表明：通过合理设计锻模，选手 坯料尺寸，能有效防止 件内部冶金缺陷的进上步扩大。计算机模拟分析是准确预测和解释 造过程内部缺陷变化的可靠手段。     

Aluminum alloy foam core sandwich panels fabricated from die casting aluminum alloy by friction stir welding route

An aluminum foam sandwiches (AFSs) consisting of ADC12 Al–Si–Cu die casting aluminum alloy foam and ADC6 Al–Mg die casting aluminum alloy face plates were fabricated. Using ADC12 die casting plates containing large amounts of gases as the starting material of the foam, ADC12 foam can be fabricated without using a blowing agent. Using FSW, both the uniform dispersion of the segregated gases and pore stabilization powder in the ADC12 die casting plates used to fabricate a foamable ADC12 precursor and the bonding of the ADC12 precursor to the ADC6 plates can be simultaneously achieved. Namely, the AFS precursor is expected to be obtained in fewer processing steps. From the visual observation of the fabricated AFSs, no deformation of the ADC6 plates occurred and the ADC6 plates on both sides of the aluminum foam remained parallel. From the X-ray CT observation of the fabricated AFSs, good pore structures without the infiltration of ADC12 foam into the ADC6 plates can be obtained at a holding temperature of 948 K and holding times of t = 10 and 11 min. In tensile tests on the fabricated AFSs, fracture occurred in the ADC12 foam parts but no fractures were observed at the bonding interface between the ADC12 foam and the ADC6 plates, that is, good bonding was obtained between the ADC12 foam and the ADC6 plates.     

Using ECAP to achieve grain refinement, precipitate fragmentation and high strain rate superplasticity in a spray-cast aluminum alloy

An aluminum 7034 alloy, produced by spray casting and with an initial grain size of ˜2.1 μm, was processed by equal-channel angular pressing (ECAP) at 473 K to produce an ultrafine grain size of ˜0.3 μm. It is shown that the rod-like MgZn₂ precipitates present in the as-received alloy are broken into very small spherical particles during ECAP and these particles become distributed reasonably uniformly throughout the material. The presence of these fine MgZn₂ particles, combined with a distribution of fine Al₃Zr precipitates, is very effective in restricting grain growth so that submicrometer grains are retained at elevated temperatures up to at least ˜670 K. Tensile testing of the pressed material revealed high elongations to failure, including elongations of >1000% when testing at a temperature of 673 K at initial strain rates at and above 10⁻² s⁻¹. These results confirm the occurrence of high strain rate superplasticity in the spray-cast alloy.     

Porosity formation in aluminium alloy castings under quasi-directional solidification

There is a significant variation in the amount of porosity found in directionally solidified castings. The porosity is least at the chill and increases towards the riser. A recent publication has suggested that this porosity distribution is caused by the rejection of hydrogen into the liquid during freezing, which results in chemical macrosegregation of dissolved gas along the length of the casting. Experiments were conducted using five aluminium-based alloys in order to test this hypothesis. The results show that chemical macrosegregation of dissolved hydrogen does not occur to any measurable degree. Instead, the observed distribution of porosity appears to be caused by effects related to changes in solidification rate and dendrite arm spacing. A simple “thermodynamic” model, which includes the effect of surface tension of the pore bubble, accounts for general features of the porosity distribution.     

Thermal and flow modelling of ladling and injection in high pressure die casting process

Air entrapment and premature solidification in the shot sleeve of the cold chamber high pressure die casting process are problems affecting the casting quality. These issues are addressed from several viewpoints, including heat loss during metal ladling, turbulence generation and gas escape during pouring, wave formation and propagation during metal pouring and injection, and heat loss and solid creation in the shot sleeve during metal injection. Measurements and simulations have been conducted for a typical industrial case where the fill ratio of the shot sleeve is about 30%. It has been found that the settling time of the aluminium alloy in the shot sleeve has a profound influence on the air entrapment. The settling time also has a negative effect on the metal quality the solid formation (premature solidification or cold flakes) in the shot sleeve. Fast pouring and quick injection (no settling time) are recommended as a good approach to minimise the air entrapment and cold flakes in the shot sleeve in this particular case. IJCMR/474     

Performance evaluation of PVD coatings for high pressure die casting

During high-pressure die-casting (HPDC) of aluminium alloys, there is a tendency for the molten alloy to react with the tool steel die, core pins and inserts. This occurrence within the high pressure die casting (HPDC) industry is referred to as ‘soldering’. It is of concern to high-pressure die casters because of down-time due to the regular removal of the soldered layer and its detrimental affect on die life and casting quality. In this investigation, several physical vapour deposited (PVD) coatings, namely, TiN, CrN and TiCN, were evaluated for their ability to eliminate soldering during HPDC of aluminium alloys. Accelerated semi-industrial trials were carried out in a 250-t Toshiba HPDC machine using a specially designed die made of P20 tool steel with removable core pins. The results from these trials showed that PVD coatings can act as a physical barrier coating preventing any reaction between the molten aluminium alloy and the tool steel. Thus the problem of soldering on such tools as core pins can be eliminated in high HPDC of aluminium alloys. In the accelerated trials, it was found that soldering was replaced by a built-up layer of cast aluminium alloy, which was less detrimental to tool life and reduced machine down-time due to the reduced need for tool polishing. The experimental results were confirmed by conducting in-plant HPDC trials.     

Microstructural characteristics of the surface layer in high-pressure die castings

A thin layer of distinct microstructure, commonly called the surface layer, is often present near the surface of high-pressure die cast (HPDC) components. Although the surface layer formation has been previously investigated, its salient microstructural features in recent studies are significantly different. Therefore, this research aims to gain a better understanding of the surface layer’s microstructural characteristics and the surface layer formation. Microstructural analysis was performed on complex-geometry, industrial-part Al-11Si-2Cu-1Fe (ADC12) and Zn-4Al (Zamak3) HPDC specimens and Al-5Mg-2Si-0.7Mn U-shaped HPDC specimens. The characterized microstructural features suggest that the surface layer starts to form during die filling and becomes stagnant at the die wall. When the inner material moves past the surface layer, primary crystals in the inner material migrate away from the surface layer, resulting in a region adjacent to the surface layer containing only solute-enriched liquid. The solute-enriched liquid in this region subsequently solidifies into the surface-layer edge.     

Superplastic behavior of a 7055 aluminum alloy

It is shown that a high strength 7055 aluminum alloy with partially recrystallized initial structure exhibits superplastic behavior in the temperature interval 400–490 °C within a wide strain rate range from 8.3×10⁻⁵ to 3.3×10⁻² s⁻¹. Maximum total elongation of about 960% and strain rate sensitivity coefficient, m, of 0.6 were obtained at a temperature of 450 °C and a strain rate of 3.3×10⁻⁴ s⁻¹.     

Fabrication and mechanical properties of high-performance aluminum alloy

High-performance Al–Cu–Mg alloy was fabricated by high-energy ball milling, sintering, and hot extrusion. The microstructure and mechanical properties of the material were preliminarily investigated. Results show that the formation of liquid phase during sintering promotes the densification of the aluminum powders. A97.1 % theoretical density is achieved in this alloy after sintering. The material shows excellent mechanical properties after extrusion and heat treatment. The ultimate tensile strength and yield strength of the extruded samples with heat treatment are 613 and 465 MPa, respectively.     

铝合金壳盖压铸工艺优化研究

通过对铝合金壳盖压铸件进行实体造型,采用铸造数值模拟软件Z-Cast对铝合金壳盖压铸过程的压力场、速度场和温度场进行数值模拟,根据模拟结果分析浇注系统和溢流槽尺寸的合理性,重新设计、优化浇注系统的形状和布置位置,得到合理的压铸方案。对于铝合金压铸件结构和压铸工艺设计有着重要的指导意义。     

An experimental study of heat transfer in aluminum castings during water quenching

The influence of quenching orientation and agitation conditions on heat transfer of aluminum alloys during water quenching was experimentally investigated with a test casting. The results indicate that heat transfer in water quenching of casting aluminum alloy consists of film boiling, nucleate boiling and convection stages. The highest heat transfer coefficients (HTC) are observed in the nucleate boiling, while the lowest is in the convective cooling stage. The heat transfer coefficients on the horizontal surfaces facing down during quenching are lower than those of other surfaces regardless whether the water is agitated or not. Agitation enhances heat transfer process especially when castings are at high temperatures and heat transfer process is in the film boiling stage.     

大型双鼓形铝轮毂精密锻模设计与改进

以载重车用大型双鼓形铝轮毂精密模锻为应用对象，开发了分体组合式锻模工装，突破了普通模锻以单一最大水平投影面分模的限制，解除了双鼓形外形对模锻成形工艺的制约，并采用80000kN电动螺旋压力机进行精密模锻，保证了产品成形精度。     

特高压产品厚大法兰类铝合金铸件的工艺研究

特高压产品厚大法兰类铸件,原工艺采用金属型简易模具生产,易出现氧化夹渣、窝气、变形等铸造缺陷。通过优化工艺方案,采用倾转式金属型重力铸造方法来生产,不仅使铸件的质量有了质的飞跃(合格率由原来的40%提高到了99%),更大大提高了铸件的生产效率及工艺出品率,且操作方便,并降低了成本,实现了“三高”(高质、高量、高效)生产,满足了日益提高的质量要求。     

Strengthening technology and mechanism for semi-solid die casting of aluminum alloy

Combined with theoretical evaluation,an optimized strengthening process for the semi-solid die castings of A356 aluminum alloy was obtained by studying the mechanical properties of castings solution treated and aged under different conditions in detail,then,the semi-solid die castings and liquid die castings were heat treated with the optimized process.The results show that the mechanical properties of semi-solid die castings of aluminum alloy are superior to those of the liquid die castings,especially the strengthening degree of heat treated semi-solid die castingsis much greater than that of liquid die castings with the tensile strength more than 330 MPa and the elongation more than 10％,and this is mainly contributed to the non-dendritic and more compact microstructure of semi-solid die castings.The strengthening mechanism of heat treatment for the semi-solid die castings of A356 aluminum alloy is due to the dispersive precipitation of the second phase(Mg2 Si) and formation of GP Zone.