过共晶铝硅合金的细化变质

根据Ａｌ－Ｓｉ二元系相图〔１〕分析了过共晶铝硅合金的主要性质。介绍了过共晶铝硅合金的细化变质方法和进展。     

铝硅合金低温加硅研究

扼要介绍了铝硅合金生产中的五种熔配工艺,以共晶型与过共晶型两种不同牌号的铝硅合金为例阐述了低温加硅熔炼技术,获得了最佳工艺,该方法质量稳定、节约能源、环境友好。     

过共晶铝硅合金的研究进展

文章从变质处理、快速凝固、超声波处理、半固态处理等方面对过共晶铝硅合金组织的影响和力学性能的改善进行了介绍,为过共晶铝硅合金的研究人员提供参考.     

国外信息

过冷对气雾化Al-Si合金粉的影响中图分类号:TF123·7文献标识码:D试验目的:研究过冷对雾化过共晶成分铝-硅合金颗粒显微结构的影响,试验方法:以氮气或氦气雾化法制取Al-Si合金粉,将制取的粉末过筛分类,按2·5 ml硝酸、1·5 ml盐酸、1 ml氢氟酸和95 ml水的比例配置腐蚀液,并对粉末样品进行腐蚀处理。在腐蚀处理后的铝-硅合金粉末样品上覆金膜,以扫描电镜观察铝-硅合金粉末样品,扫描电镜的电子加速电压是20kV。金相分析结果表明:在过冷度低的情况下,在液态粉末颗粒中硅先结晶,接着在硅晶核的表面形成富铝区,在富铝区外形成很宽的共晶区。…     

中铝公司过共晶铝硅合金技术达国际先进水平

中铝公司"替代进口发动机用新型过共晶铝硅合金的开发"项目通过中国有色金属工业协会专家鉴定,专家认为项目整体技术达到国际先进水平。该项目建立了一条挤压铸造中试线,为过共晶铝硅合金活塞和缸套的制造提供了经济可行的技术,可用于汽车、轮船     

含镍的过共晶铝硅合金的砂型铸造方法

正欧洲专利WO2014158384本专利提供一种含3.0%~6.0%Ni的过共晶铝硅合金,但不含Fe、Cu、Mn等元素,可用于砂型铸造,特别是消失模铸造,其耐热性能和机械加工性能都很好,打破了过共晶铝硅合金在很大范围内不能用于砂型铸造的限制。     

过共晶铝硅合金新型变质剂的研究

通过拉伸实验和金相观察,研究了过共晶铝硅合金新型变质剂的时效性,以及不同变质时间和添加顺序对变质效果的影响。试验表明:自制新型变质剂对过共晶铝硅合金具有良好的变质效果。     

二次加热控制高硅铝合金中初生硅形态的研究

用光学显微镜(OM)及Image Pro Plus金相分析软件对半固态二次加热处理后的过共晶铝硅合金的初生硅组织特征进行分析。结果表明,在过共晶铝硅合金中,通过磷盐变质处理可以让初生硅相细化,平均直径由117μm降至31μm,并通过半固态二次加热使初生硅的形态得到显著的改善,其形状因子为0.67。     

合金625的熔融和固结

美国新墨西哥州桑迪国家实验室报道,他们在已试验过的合金625样品中发现,含有铌的这种合金试样具有含NbC、拉维斯相和MgC型金属碳化物的极限共晶型成分。与基本成分相同但不含铌的合金相比,这种镍基合金具有广宽的熔融/固结温度范围和减少抗热断裂性能,含铌合金中添加碳和硅可增加共晶成分的数量,并提高对热断裂的敏感性;而无铌合金中添加碳和硅可增大合金的熔融/固结温度范围和对热断裂的敏感性。     

中铝公司一项目技术达国际先进水平

近日，中铝公司“替代进口发动机用新型过共晶铝硅合金的开发”项目通过中国有色金属工业协会专家鉴定，专家认为项目整体技术达到国际先进水平。该项目建立了一条挤压铸造中试线，为过共晶铝硅合金活塞和缸套的制造提供了经济可行的技术，可用于汽车、轮船等交通领域钢铁材料的替代，节能减排效果显著。     

Effect of neodymium on primary silicon and mechanical properties of hypereutectic Al-15%Si alloy

The mechanical properties of hypereutectic Al-Si alloys are mainly determined by size and morphology of the primary silicon phase.So,optical microscopy(OM) and X-ray diffraction(XRD) were adopted to study affection of Nd on primary silicon of hypereutectic Al-15%Si alloy in this paper.The results of OM showed that pure Nd could effectively refine primary silicon of hypereutectic Al-15%Si alloy.When Nd addition was 0.3%,the average size of primary silicon reduced from 20-40 μm of initial sample to 10-20 μm of modified sample.XRD pattern showed that no new phase was formed after Nd modification.The results of mechanical properties test showed that whole properties of modified samples were significantly improved.Tensile strength increased about 32.6% from 147 MPa to 195 MPa.Elongation was increased about 160% from 1.0% to 2.6%.The improvement of mechanical properties should attribute to primary silicon refinement after modification.     

The effect of fluid flow on eutectic growth

The effect of fluid flow on eutectic microstructure is systematically examined in Al-Cu alloys of compositions varying from 19.5 to 45.0 wt pct Cu. It is shown that significantly different fluid-flow effects are present in hypo- and hypereutectic alloys, since the modes of convection are different in these two cases. In hypoeutectic alloys, the rejected solute is copper, which is heavier than aluminum, and fluid flow gives rise to radial solute segregation in cylindrical samples. In hypereutectic alloys, a lighter aluminum is rejected that causes a double diffusive convection and gives rise to macrosegregation. These composition variations are shown to produce nonuniform microstructures that vary either radially (in hypoeutectic alloys) or axially (in hypereutectic alloys) and can give rise to a single phase-to-eutectic, lamellar-to-rod eutectic, or rod-to-lamellar eutectic transition in a given sample. Composition measurements are carried out to characterize solute segregation due to fluid flow. The fluid-flow effect on eutectic spacing in eutectic or near-eutectic alloys is found to be very small, whereas it increases the eutectic spacing in hypoeutectic alloys for a given local composition and it can increase or decrease the spacing in hypereutectic alloys, depending on the microstructure and solidification fraction. Theoretical models, based on diffusive grwoth, are modified to predict the spatio-temporal variation in eutectic microstructure caused by fluid flow.     

Effect of neodymium on primary silicon and mechanical properties of hypereutectic Al-15%Si alloy

The mechanical properties of hypereutectic Al-Si alloys are mainly determined by size and morphology of the primary silicon phase. So, optical microscopy (OM) and X-ray diffraction (XRD) were adopted to study affection of Nd on primary silicon of hypereutectic Al-15%Si alloy in this paper. The results of OM showed that pure Nd could effectively refine primary silicon of hypereutectic Al-15%Si alloy. When Nd addition was 0.3%, the average size of primary silicon reduced from 20-40 μm of initial sample to 10-20 μm of modified sample. XRD pattern showed that no new phase was formed after Nd modification. The results of mechanical properties test showed that whole properties of modified samples were significantly improved. Tensile strength increased about 32.6% from 147 MPa to 195 MPa. Elongation was increased about 160% from 1.0% to 2.6%. The improvement of mechanical properties should attribute to primary silicon refinement after modification.     

Review of Microstructure Evolution in Hypereutectic Al–Si Alloys and its Effect on Wear Properties

Al–Si alloys with silicon content more than 13 % are termed as hypereutectic alloys. In recent years, these alloys have drawn the attention of researchers due to their ability to replace cast iron parts in the transportation industry. The properties of the hypereutectic alloy are greatly dependent on the morphology, size and distribution of primary silicon crystals in the alloy. Mechanical properties of the hypereutectic Al–Si alloy can be improved by the simultaneous refinement and modification of the primary and eutectic silicon and by controlling the solidification parameters. In this paper, the effect of solidification rate and melt treatment on the evolution of microstructure in hypereutectic Al–Si alloys are reviewed. Different types of primary silicon morphology and the conditions for its nucleation and growth are explained. The paper discusses the effect of refinement/modification treatments on the microstructure and properties of the hypereutectic Al-Si alloy. The importance and effect of processing variables and phosphorus refinement on the silicon morphology and wear properties of the alloy is highlighted.     

Production of High-Quality Bars of Hypereutectic Silumins by Helical Rolling

A study is made of the possibility of improving the structure and properties of hard-to-deform hypereutectic silumins with the use of helical rolling (HRG) on the PVP 20-60 universal mill at the All-Union Scientific Research Institute of Light Alloys. The parameters of hot HRG are optimized by numerically modeling the deformation process in a three-high stand. The resulting data is confirmed experimentally by subjecting standard hypereutectic silumins 01390 and 01391 to HRG. The use of HRG makes it possible to refine the structure of hypereutectic silumins and improve their mechanical properties.     

合金化Cr优化含Fe过共晶Al-Si合金显微组织及其机制

采用传统铸造工艺和喷射成形技术制备了无Cr和含Cr的含Fe过共晶Al-Si合金,并利用SEM(EDS)、XRD及DSC对其显微组织、相组成及相变过程进行了研究。结果表明:2%Cr的加入不光使铸态粗大针片状的δ-Al4FeSi2相变为"骨骼状"α-Al(Fe,Cr)Si相,而且使沉积态Al-25Si-5Fe-3Cu合金中短棒状的富铁相(～10μm左右)被尺寸小于3～5μm的颗粒状α-Al(Fe,Cr)Si相所替代,从而细化的组织更有利于合金性能的提高。等温处理实验结果显示沉积态含Cr合金具有较好的组织热稳定性,其主要归因于颗粒状α-Al(Fe,Cr)Si相自身的高温稳定性,而沉积态Al-25Si-5Fe-3Cu合金热稳定差主要由于β-Al5FeSi相的长大和A7Cu2Fe相的形成。另外,结合显微组织和喷射成形工艺特点对沉积态组织形成机制分析发现α-Al(Fe,Cr)Si相有可能通过直接从液相析出和经δ-Al(Fe,Cr)Si相转变而来。     

Growth characteristics of directionally solidified Al203/YAG/ZrO2 ternary hypereutectic in situ composites under ultra-high temperature gradient

Oxide eutectic ceramic in situ composites have attracted significant interest in the application of high-temperature structural materials because of their excellent high-temperature strength,oxidation and creep resistance,as well as outstanding microstructural stability.The directionally solidified ternary Al_2O_3/YAG/ZrO_2 hypereutectic in situ composite was successfully prepared by a laser zone remelting method,aiming to investigate the growth characteristic under ultra-high temperature gradient.The microstrucnrres and phase composition of the as-solidified hypereutectic were characterized by using scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and X-ray diffraction(XRD).The results show that the composite presents a typical hypereutectic lamellar microstructure consisting of fine A1203 and YAG phases,and the enriched ZrO_2 phases with smaller sizes are randomly distributed at the Al2O3/YAG interface and in Al_2O_3 phases.Laser power and scanning rate strongly affect the sample quality and microstructure characteristic.Additionally,coarse colony microstructures were also observed,and their formation and the effect of temperature gradient on the microstructure were discussed.     

Investigation into the structure and phase composition of powder aluminum-phosphorus master alloys

Powder aluminum-phosphorus master alloys for modifying hypereutectic silumins are developed. Optimal treatment modes of powder mixtures in a high-energy planetary mill which give minimal losses of the starting material and the microstructure with the uniform and dispersed distribution of particles of excess phases in the aluminum matrix are selected. The phase composition of formed master alloys is investigated by electron probe microanalysis. The high efficiency of modifying the hypereutectic silumin Al-17 wt % Si by introducing phosphorus (0.008 wt %) using fabricated master alloys is shown.     

Microstructural and microhardness characteristics of laser-synthesized Fe-Cr-W-C Coatings

The effects of laser-processing parameters on the microstructure and microhardness of Fe-Cr-W-C quaternary alloy coatings were investigated experimentally. The coatings were developed by laser processing a powder mixture of Fe, Cr, W, and C at a weight ratio of 10:5:1:1 on a low-carbon steel substrate using a 10 kW continuous wave CO₂ laser. Depending on the processing parameters, either hypoeutectic or hypereutectic microstructures were produced. The hypoeutectic microstructures comprised primary dendrites of nonequilibrium face-centered cubic (fcc) austenite γ phase and eutectic consisting of pseudohexagonal close-packed (hcp) M₇C₃ (M = Cr, Fe, W) carbides and fcc γ phase. The hypereutectic microstructures consisted of hcp M₇C₃ primary carbides and eutectic similar to that in the hypoeutectic microstructures. The formation of hypoeutectic or hypereutectic microstructures was influenced by the alloy composition, particularly the C concentration, which depends on the amount of powder delivered into the melt pool and the extent of substrate melting. The enhancement of the lattice parameter of the γ phase is associated with the significant dissolution of alloying elements and lattice strains resulting from rapid quenching. The higher hardness of the hypereutectic microstructures is principally attributed to the formation of hcp M₇C₃ primary carbides. The relatively lower hardness of the hypoeutectic microstructures is related to the presence of y phase in the primary dendrites, excessive dilution from the base material, and relatively low concentrations of Cr and C. The results provide insight into the significance of laser-processing conditions on the composition and hardness of Fe-Cr-W-C alloy coatings and associated solidification characteristics.