钛对AlSi7Mg0.3合金力学性能的影响

研究了钛对ＡｌＳｉ７Ｍｇ０．３合金金相组织和力学性能的影响。钛量超过０．１２％，铝合金晶粒不再细化，而冲击韧度和伸长率急剧下降，抗拉强度缓慢上升，硬度变化甚微。力学性能如此变化可能是出现针状钛相造成的。ＡｌＳｉ７Ｍｇ０．３合金最佳钛量应在０．０８％～０．１０％范围内。此时，铁含量接近０．１８％。

AlSi7Mg0.3/SiC_p复合材料低压铸造

介绍了颗粒增强铝基复合材料低压铸造的优越性及过程的动态特征。试验测定了含SiC15 %(体积分数 )、基体合金为AlSi7Mg0 .3的复合材料重力铸造和低压铸造的流动性、抗拉强度、延伸率。

钇基重稀土对AlSi7Mg0.3合金组织和性能的影响

采用钇基重稀土对AlSi7Mg0.3合金进行了细化变质处理,研究了钇基重稀土对合金组织、热处理态力学性能的影响。实验表明: 钇基重稀土能强烈变质AlSi7Mg0.3合金中的共晶硅,同时对初晶α(Al)有明显的细化作用,使合金的力学性能得到大幅提高。

Preparation of semisolid AlSi7Mg alloy slurry through weak traveling-wave electromagnetic stirring

The semisolid AlSi7Mg alloy slurry with large capacity was prepared by low superheat pouring and week traveling-wave electromagnetic stirring. The effects of electromagnetic stirring power and frequency on the shape and distribution of primary α-A1 grains in the AlSi7Mg alloy slurry were discussed. The experimental results show that the AlSi7Mg alloy slurry with fine and spherical primary α-A1 grains distributed homogeneously can be obtained. Under the condition of low superheat pouring and week traveling-wave electromagnetic stirring, when the pouring temperature is 630℃, raising the stirring power or frequency appropriately can gain a better shape of primary α-Al grains; but if the stirring power or frequency is increased to a certain value （1.72 kW or10 Hz）, the shape of primary α-A1 grains cannot be obviously improved and spherical primary α-Al grains distributed homogeneously can be still obtained.

New method for the preparation of semi-solid AlSi7Mg alloy slurry

The effects of pouring temperature and short electromagnetic stirring with low strength on the microstructures of AlSi7Mg alloy were investigated. The results show that if liquid AlSi7Mg alloy is poured at 630 or 650℃, many primary α-Al grains in the solidified melt are rosette-like, and only a small number of them are spherical. However, if liquid AlSi7Mg alloy is poured at a lower superheat and meanwhile is stirred by an electromagnetic field at a low power for a short time, then most primary α-Al grains in the solidified melt become spherical, and only a few are rosette-like. The theoretical analysis indicates that the strengthened melt flow motion induced by the short electromagnetic stirring makes the temperature field more homogeneous in the melt, which is poured at a lower superheat, and makes the primary α-Al grains deposit in a larger region at the same time, so this new solidification kinetic condition leads to the microstructure of spherical primary α-Al grains. The experiments also demonstrate that pouring at an appropriate superheat and stirring by an electromagnetic field at a low power for a short time is a good new method for preparing the semi-solid slurry or billet of AlSi7Mg alloy.

Effect of pouring height on the solidified microstructure of AlSi7Mg alloy

The effect of different pouring heights and evenly soaking process in the liquidus and solidus range on the solidified microstructure of AlSi7Mg alloy has been studied. The results show that if the pouring temperature is 630 or 650℃ and the pouring height is 40 mm, the microstructure of the solidified melt is not homogeneous and there are many rosette-like primary α-Al grains. But if the pouring height is increased to 400 mm, the solidified microstructure becomes more homogeneous and favorable to obtain spherical primary α-Al grains in the solidified melt. With further being evenly soaked in the liquidus and solidus range for some time, the temperature difference between the melt center and the melt periphery can be controlled within ±2℃ and the primary α-Al grains will evolve into more spherical grains. The theoretical analysis indicates that the higher pouring height promotes the melt flow motion and makes the temperature field in the melt more homogeneous and restrains the large rosette primary α-Al grains. This flow motion can also promote the ripening effect and the primary α-Al grains in the melt are gradually changed into spherical grains. It can be concluded from the experiments that pouring at an appropriate superheat and from a proper height is a good new method for preparing the semisolid slurry of AlSi7Mg alloy, its process control is easy and the preparation cost is lower.

铸造铝合金AlSi7Mg0.3应力腐蚀性能研究

利用拉伸测试,剥落腐蚀性能及扫描电镜分析等手段,研究了AlSi7Mg0.3合金的应力腐蚀性能。结果表明:合金材料其剥落腐蚀等级评定为PA级,其耐剥落腐蚀性能良好;合金材料试样在室温与50℃的3.5%NaCl腐蚀溶液介质中应力腐蚀敏感性相对较小;在室温和50℃空气中和3.5%NaCl盐水中进行拉伸时呈现出典型的韧性断裂特征。

Microstructure and properties of AlSi7Mg alloy fabricated by selective laser melting

The AlSi7Mg alloy was fabricated by selective laser melting(SLM),and its microstructure and properties at different building directions after heat treatment were analyzed.Results show that the microstructure of SLM AlSi7Mg samples containes three zones:fine grain zone,coarse grain zone,and heat affected zone.The fine-grain regions locate inside the molten pool,and the grains are equiaxed.The coarse-grain regions locate in the overlap of molten pools.After T6 treatment,the microstructure at the molten pool boundary is still the network eutectic Si,but the network structure becomes discrete,and is composed of intermittent,chain-like eutectic Si particles.The yield strength at three directions(xy,45°,z direction)of the AlSi7Mg alloy samples fabricated by SLM is improved after T6 heat treatment.The fracture mechanism of the samples is a mixed ductile and brittle fracture before heat treatment and ductile fracture after heat treatment.

轨道交通用大型铝合金齿轮箱铸件的研制

根据高铁复兴号用大型铝合金齿轮箱铸件的结构特点和技术要求,采用树脂砂造型及低压浇注方式,合理地设计浇注系统、冒口、冷铁及低压浇注工艺,并结合CAE仿真技术进行分析和工艺优化,成功解决了缩孔、缩松和气孔缺陷。最终研制的铝合金齿轮箱力学性能良好,内外在质量高,能够满足速度160km/h动力集中型动车组列车运行的需要。

Preparation for Semi-Solid Aluminum Alloy Slurry under Weak Electromagnetic Stirring Conditions

The effects of pouring temperature, short electromagnetic stirring with low strength and then soaking treatment on the microstructure of AISi7Mg alloy were investigated. The results show that if AlSi7Mg alloy is poured at 630 or 650℃ and meanwhile stirred by an electromagnetic field at a low power for a short time, the pouring process can be easily controlled and most solidified primary α-Al grains become spherical and only a few of them are rosette-like. Weak electromagnetic stirring makes the temperature field more homogeneous and makes the primary α-Al grains disperse in a larger region, which leads to the spherical microstructures of primary α-Al grains. When the AISi7Mg alloy is soaked or reheated at the semisolid state, the primary α-Al grains ripen further and they become more spherical, which is favorable to the semi-solid forming of AlSi7Mg alloy.

Microstructures of an AlSi_7Mg alloy by near-liquidus casting

Semi-solid ingots of an A1SiTMg alloy were obtained using the method of near liquidus casting. Their microstructures exhibit the characteristics of free, equiaxed, and non-dendrite, which are required for semi-solid forming. The influences of casting temperature, heat preservation time, and cooling rate on the microstructure were also investigated. The results show that in the temperature region near liquidus the grain size becomes small with a decrease in casting temperature. Prolonging the heat preservation time makes grain crassitude at the same temperature. And increasing the cooling rate makes grain fine. The microstructure of the alloy cast with iron mould is freer than that with graphite mould.

Effect of Pouring Process on the Microstructures of Semi-Solid AlSi_7Mg Alloy

The effect of different pouring temperatures and different pouring heights, the distance between the mouth of the pouring ladle and the top of the mold, on the microstructure of AlSi7Mg alloy have been researched in the paper. When the pouring temperature is close to the liquidus temperature, the primary alpha -Al in 'the billets of AlSi7Mg alloy solidified into spherical and nodular fine grains distributed homogeneously. The optimum pouring temperature for semi-solid AlSi7Mg billet with spherical or nodular primary alpha -Al is 615 degreesC. At the same pouring temperature, the higher the pouring ladle, the more easily the spherical and nodular primary alpha -Al obtained in the semi-solid AlSi7Mg billet. When the pouring temperature is close to the liquidus temperature and the pouring ladle is relatively high, it is the great cooling rate, the flow of the molten allay caused by pouring and the large simultaneous solidification region induced by the near liquidus temperature, that promote the formation of spherical or nodular primary cr-Al.

Continuous cooling precipitation diagram of cast aluminium alloy Al-7Si-0.3Mg

The precipitation behaviour during quenching of cast Al-7Si-0.3Mg aluminium alloy was investigated by DSC in the cooling rate range of 0.01 K/s to 3 K/s and by quenching dilatometry for higher rates. Two main precipitation reactions were observed during cooling, a high temperature reaction starting almost directly with quenching from 540℃ and a low temperature reaction starting at about 400℃. Quenching with 3 K/s already significantly suppresses precipitation during quenching. Hardness after T6 ageing increases with increasing quenching rate, due to the increasing content of supersaturated solid solution. By dilatometry and hardness results the critical cooling rate can be estimated as about 60 K/s. Quenched Al-7Si-0.3Mg microstructures have been investigated by light microscopy. The microstructures consist of an aluminium-silicon eutectic structure, aluminium solid solution dendrites and precipitates inside the aluminium dendrites, depending on quenching rate.

Effect of withdrawal rate on microstructure of a hypoeutectic Al-Si alloy by low superheat DC casting

To obtain the billet with homogeneous and spheroidized primary grains is the key step in the semi- solid forming process. Among the semi-solid billet preparation methods, the process of low-superheat direct chill （DC） casting is simpler and more effective. In this study, the billets of AISi7Mg alloy were prepared by low- superheat DC casting at various withdrawal rates. The effect of withdrawal rate on the surface quality of the billets was investigated, and the evolution mechanism of the microstructural morphology in the billets was analyzed. The results show that the periodic corrugations and a large quantity of fine shrinkage pits appear in the billet surface when the withdrawal rate is 100 mm.min-1, and the above defects in the billet surface can be eliminated completely when the withdrawal rate is above 150 mm.min-1. But when the withdrawal rate is too fast （250 mm.min-1）, the primary a grains, except the ones in the billet center, have not enough time for ripening due to the high silidification rate, and will solidify as the dendrite structure. When the withdrawal rate is between 150 - 200 mm.min-1, the dendritic growth of the primary a grains is effectively inhibited, and a billet of AISi7Mg alloy with a smooth surface and homogeneous, fine, non-dendritic grains can be obtained.

Electro-pulse modification and reheating process for production of thixotropic microstructure in AlSi_7Mg alloy

Electro-pulse modification(EPM) was used to change the dendritic structure of AlSi7Mg alloy to globular one.The effects of the modified temperature,electro-pulse frequency and time on the solidified structure were examined.The results show that these parameters play an important role in the solidified microstructures.That is to say,under the same modified temperature,the solidified microstructure will be improved greatly with the increase of electro-pulse frequency and time,but when they exceed to limit values,the solidified microstructure will become worse,resulting from the decrease of the ratio of nucleation.The experimental results indicate that the suitable modified temperature of AlSi7Mg alloy is 720 °C,and the appropriate electro-pulse frequency and time are 5 Hz and 40 s,respectively.Then the microstructures produced by suitable EPM process were reheated at temperatures between liquidus and solidus,the primary-Al grains ripen further and become more spherical,which is favorable to the semi-solid forming of AlSi7Mg alloy.

高速动车组铝合金齿轮箱低压铸造工艺研究

介绍了高速动车组齿轮箱箱体的结构特点和技术要求,概述了箱体研制所采用的低压铸造工艺。对试制中出现的气孔、针孔及缩孔缩松等典型缺陷进行判定和分析,并通过MAGMAsoft软件进行箱体铸造工艺模拟分析和优化,进而采取有效措施成功解决了气孔、针孔及缩孔缩松缺陷,开发出质量稳定可靠的高速动车组铝合金齿轮箱,运用于同类型多种产品。

Evolution of globular microstructures during processing of aluminium slurries

Slurry processing experiments were performed with AlSi7Mg0.6 to identify the globularization mechanisms.The melt sample water quenched slightly above the liquidus point is predominantly dendritic while that cooled into the semi-solid temperature range internally via stirring the melt with a rotating cylindrical block of the alloy itself becomes fully globular.The globules are much smaller when internal cooling and stirring are employed longer to achieve higher solid fractions before casting.Coarse dendrite fragments of various sizes are revealed,in the case of stirring after an initial fraction of solid is first formed without the benefit of additional internal cooling.

稀土Y对AlSi_7Mg_(0.3)合金组织和力学性能的影响

采用稀土Y对AlSi_7Mg_(0.3)合金进行了变质处理,借助金相显微镜、X射线衍射仪及拉伸试验研究了稀土Y添加对AlSi7Mg0.3合金显微组织及力学性能的影响。研究结果表明,添加少量稀土Y有利于共晶Si的细化,Si相明显由板片状向针状、细小颗粒状转变;合金延伸率随着稀土Y添加量的增加呈逐渐升高趋势,当稀土Y添加量在0.06%时延伸率达到最高值12.5%。

Refining mechanism of yttrium on primary α-Al in semi-solid Al alloy

Semi-solid Al7Si0.3Mg alloy slurry, which is grain-refined by yttrium, is manufactured by low temperature pouring. The effects of grain-refined by yttrium on the morphology and the grain size of the primary α-Al in semi-solid Al7Si0.3Mg alloy are researched. The results indicate that semi-solid Al7Si0.3Mg alloy with particle-like and rosette-like primary α-Al can be prepared by low temperature pouring from liquid Al7Si0.3Mg alloy grain-refined by yttrium. The grain size and particle morphology of primary α-Al in Al7Si0.3Mg alloy are markedly improved by 0.5 wt pet Y. The refining mechanism of Y on the morphology and the grain size of the primary α-Al in semi-solid Al7Si0.3Mg alloy are delved.