强磁场对Al-18Si合金凝固组织的影响及其机理研究

研究了过共晶Al-18Si合金在稳恒强磁场中的凝固行为.实验表明,在稳恒强磁场作用下,过共晶Al-18Si合金中的初生Si发生显著偏聚.为解释初生Si的偏聚机理,建立了相应的量子理论模型.模型认为:初生Si在Al-18Si合金中的偏聚是由于部分Si原子在磁场中获得附加能后,沿磁场方向做旋进运动所致.Si原子在10T磁场中获得的附加能为1.854×10-22J.     

往复挤压Mg-4Al-2Si合金中Mg2Si颗粒形貌与分布

使用往复挤压细化Mg-4Al-2Si (AS42)合金组织,利用OM,SEM和TEM研究Mg2 Si颗粒形貌和分布特征.结果表明,铸态AS42合金中Mg2Si颗粒呈共晶汉字状和初生块状.共晶Mg2 Si经2道次往复挤压后全部破碎,且分布均匀.经6道次挤压后初生Mg2 Si颗粒全部破碎,细小的Mg2 Si颗粒已基本球化....     

喷射沉积连续挤压Al-20Si合金的微观组织及磨损性能

喷射沉积连续挤压技术是由喷射成型和连续挤压复合而成的新技术。本试验采用自制的喷射沉积连续挤压设备,在多种过热度条件下完成了Al-20Si合金的喷射沉积连续挤压试验,获得了8mm的铝合金杆件制品,分别对其显微组织和摩擦磨损性能进行研究。结果表明:喷射沉积连续挤压工艺可有效抑制初生硅的形核和生长,制备的铝硅合金中初生硅的尺寸约3~8μm,较铸态组织有明显细化,使得其耐磨性能提升1~2倍;随过热度的增加,喷射沉积连续挤压铝硅合金中初生硅的尺寸不断减小且分布更加弥散,使得合金的耐磨性更加优良。     

电磁场对A1-18%Si过共晶合金初晶Si相形貌的影响

研究了交流电场、直流磁场和二者复合产生的电磁振荡对A1-18%(质量分数)Si过共晶初晶Si相形貌的影响。结果表明:交流电场、直流磁场和电磁振荡都使合金初晶Si相的大小经历了一次细化过程,交流电场使Si原子有序偏聚团的尺寸和数目发生改变,增大形核率,细化初晶Si相;直流磁场通过电磁制动效应抑制了初晶Si相的形核与长大;电磁振荡细化作用是通过减弱合金的成分过冷和温度梯度从而增大过冷度实现的。三者相比,在电磁振荡的作用下初晶Si相更为细小。     

初生α相含量对TC18时效组织及力学性能的影响

目的 探究TC18合金中初生α相含量对时效后次生α片层形貌及力学性能的影响.方法 通过改变两相区固溶温度控制初生 α 相含量,观察固溶后合金元素分布及相同时效后合金的组织形貌,研究固溶温度对合金拉伸性能的影响.结果 固溶过程中发生元素再分配,固溶温度低,初生α相含量高,β基体中β稳定元素含量高,β基体稳定性强,抑制时效过程中次生α片层析出,时效强化效果弱.固溶温度高,β基体稳定性弱,促进时效过程中次生α片层析出,时效强化效果显著.结论 固溶温度升高,初生α相比例降低,即β基体稳定性降低,促使时效过程中大量次生α相析出,显著提高合金强度.     

交流电脉冲调控Al-7%Si合金中α-Al相形态演化机制

研究了低压交流电脉冲下Al-7%Si合金初生α-Al相的微观组织演化规律,数值模拟了合金熔体中的电流及电磁力分布,结合模型中嵌入金属网的方法,对电脉冲调控微观组织的机理进行了分析。结果表明,无论砂型还是金属网内、外,α-Al树枝晶随着脉冲电流密度的增大而更细化,然而部分组织形貌由树枝状向蔷薇状的转变与脉冲电流密度和位置都有关。相同的电脉冲下,当脉冲电流密度足够大时,砂型中与金属网内、外的α-Al相组织形貌存在显著差异。分析认为,初生α-Al相组织的变化主要是由脉冲电磁力驱动的熔体对流作用引起的;此外通过计算熔体流动状态雷诺数,预测了不同密度电脉冲作用下Al-7%Si合金中初生α-Al相的形貌。     

熔体深过冷过共晶铝硅合金的凝固组织研究

本工作采用熔体急冷装置对过共晶铝硅熔体进行深过冷处理,采用光学显微镜、扫描电子显微镜和X射线衍射仪等手段,研究了硅含量和熔炼工艺对熔体深过冷过共晶铝硅合金凝固组织的影响。研究结果表明,合金在800℃熔炼,保温时间为30 min时,熔体深过冷处理可抑制Al-(14～18) Si合金熔体在凝固过程中初晶硅的析出。当Al-18Si合金在800℃熔炼,保温时间超过30 min时,深过冷Al-18Si合金熔体在室温金属模型中凝固时可完全抑制初晶硅的析出,获得无初晶硅的凝固组织。     

电磁振荡频率对半连铸7075Al合金微观组织的影响

采用同时施加一个稳恒磁场和一个交变磁场的方法，在半连铸7075铝合金过程中，使凝固熔体产生受迫振荡。实验研究了电磁振荡的频率对晶粒细化的影响规律，结果表明电磁振荡法获得的晶粒尺寸比CREM法的小，且随着电磁振荡频率降低，铸锭整体组织变得更加细小和均匀。并对电磁振荡作用下，合金凝固组织的细化机理进行了探讨。     

用行波电磁搅拌制备半固态AlSi7Mg合金浆料

用低过热度浇注和弱行波电磁搅拌工艺制备半固态AlSi7Mg合金浆料,研究了浇注温度和搅拌功率对其初生α-Al形貌的影响.结果表明,用该工艺可制备初生α-Al形貌呈小而圆整的球状晶粒,组织分布均匀,较大尺寸(直径为127 mm)的半固态AlSi7Mg合金浆料.浇注温度合适,短时间弱电磁搅拌(8 S左右)就可获得初生α-Al形貌大部分为球状,组织分布比较均匀的浆料组织.浇注温度一定,适当提高搅拌功率可明显改善初生α-Al的形貌,但是过高的搅拌功率并不能使初生α-Al的形貌进一步改善.用该工艺制备的半固态AlSi7Mg合金浆料,从其边部到心部的径向组织初生α-Al形貌经历了一个从枝晶组织向蔷薇状组织再向球状组织转变的过程.     

Preparation of semi-solid AlSi7Mg alloy slurry through traveling electromagnetic stirring

用低过热度浇注和弱行波电磁搅拌工艺制备半固态AlSi7Mg合金浆料, 研究了浇注温度和搅拌功率对其初生α-Al形貌的影响. 结果表明, 用该工艺可制备初生$\alpha$--Al形貌呈小而圆整的球状晶粒、组织分布均匀、 较大尺寸(直径为127 mm)的半固态AlSi7Mg合金浆料. 浇注温度合适, 短时间弱电磁搅拌(8 s左右)就可获得初生α-Al形貌大部分为球状, 组织分布比较均匀的浆料组织. 浇注温度一定, 适当提高搅拌功率可明显改善初生 α-Al的形貌, 但是过高的搅拌功率并不能使初生α-Al的形貌进一步改善. 用该工艺制备的半固态AlSi7Mg合金浆料, 从其边部到心部的径向组织初生 α-Al形貌经历了一个从枝晶组织向蔷薇状组织再向球状组织转变的过程.     

电磁搅拌对过共晶Al-Si合金初生Si长大过程和形貌的影响

研究了电磁搅拌对过共晶Al-Si合金中初生Si长大和形貌的影响。结果表明,当合金含Si量低于30％时,电磁搅拌引起过共晶Al-Si合金中初生Si显著细化和球团化,但当合金含Si量超过30％时,电磁搅拌对初生Si细化的作用有限,组织中仍然存在较粗大的板片状初生Si;提高电磁搅拌时合金熔体冷却速度可减小初生Si的尺寸;进行正、反转电磁搅拌,初生Si的尺寸将进一步减小,在电磁搅拌条件下,初生Si发生细化和球团化的主要原因是：搅拌引起合金熔体温度场、溶质场的均匀化,引起初生Si的机械破碎,相互摩擦和抑制初生Si各向异性生长。     

电磁铸造对Al–Si12.6%共晶合金微观组织的影响

目的 了解外加耦合场作用下Al–Si合金的微观组织演变情况。方法 利用外磁场加强凝固过程中熔体的流动,从而获得合金中各相的形态、分布和取向等,利用扫描电子显微分析技术(SEM)和电子背散射衍射分析技术(EBSD)研究电磁场对Al–Si12.6%共晶合金微观组织的影响规律。结果 在磁场作用下,铸件的组织均匀性增加,初生铝和共晶硅的尺寸均减小,并且随着磁场强度的增大,共晶硅的含量和尺寸呈减小趋势,其形态趋于等轴状,共晶硅附近各铝枝晶之间的外延生长关系消失,相互独立形核和长大。结论研究成果可以为电磁铸造对Al–Si系共晶合金微观组织研究提供一定的参考。     

Si对明弧堆焊合金M_7C_3相及耐磨性的影响

采用药芯焊丝自保护明弧焊方法制备Fe-17Cr-4C-2V-Mn-Si-Ti多元合金系堆焊合金。借助金相显微镜、X射线衍射仪及扫描电镜等手段,研究硅对其M_7C_3(M=Fe,Cr,V,Mn)相及耐磨性的影响。结果表明:当硅含量从0.6%(质量分数,下同)增加到2.4%时,初生M_7C_3相由板条状转变为块状弥散分布;其相邻间隔的γ-Fe数量逐渐减少直至消失。硅改变了初生M_7C_3形核前驱体-液态合金化高碳原子团簇的属性而引起其形态、分布和尺寸改变。磨损结果表明,当硅含量从0.6%增加至2.4%时,合金耐磨性先提高后下降,至1.5%时耐磨性最佳,微切削和微观断裂两种磨损机理并存。     

Effect of Zn addition on primary silicon morphology and B distribution in Si–Al alloy

Si–Al–Zn alloy melts were used for silicon purification by the solvent refining process. The effect of metal Zn addition on alloy macrostructure, primary Si morphology, as well as B distribution in Si–Al alloy during solvent refining process was studied in this work. The three main results were as follows. First, with the increasing of Zn content in Si–Al alloy, the primary silicon changed from slender plate-like to irregular and short, meanwhile the distribution of primary silicon changed from bottom to central and top. Second, the more Zn content in Si–Al alloy, the more inclusions of eutectic melts will be in primary silicon, which results in diffusion difficulty of impurity B in inclusions. Third and last, with increasing Zn content, the refining ratio of B increased gradually and removal fraction of B decreased accordingly.     

电磁搅拌频率对半固态A356初生α相的影响

利用低过热度浇注和电磁搅拌技术制备半固态A356铝合金浆料。采用变频技术控制电磁搅拌装置,探讨了电磁搅拌频率对半固态初生α相形貌的影响;通过数值模拟获得了磁感应强度较强的电磁搅拌频率。研究结果表明,在半固态A356合金浆料的制备过程中,电磁搅拌频率对半固态初生相的形貌影响很大,通过实验研究获得了制备半固态A356铝合金浆料的合适工艺参数,即在浇注温度620℃、保温温度590℃、保温时间10min、搅拌时间15s的条件下,搅拌频率为30Hz的晶粒细化效果最佳,其平均形状因子为0.80,平均等级圆直径为76.1μm。     

Influence of Silicon Morphology and Mechanical Properties of Piston Alloys

In this paper, the influence of silicon particle morphology on mechanical properties of two piston alloys has been reported. Alloys having nominal composition Al-12%Si-1%Ni-0.8%Cu-0.6%Mg (LM13) and Al-17%Si-1%Ni-0.8%Cu-0.6%Mg (LM28) were prepared by melting and casting. The morphology of silicon crystals was changed using additives during the melt treatment and subsequently by heat treatment. Mechanical properties such as hardness, ductility, and tensile strength of experimental alloys were tested. Test results showed that the melt treatment and heat treatment of both the alloys increased the tensile strength, hardness, and ductility. However, the influence of melt treatment on mechanical properties was not as significant as that of heat treatment. Tensile strength and ductility of LM13 was found to be higher than the LM28 alloy under similar conditions. Hardness of LM28 was higher than the LM13 alloy. Optical and SEM studies showed a change in eutectic silicon morphology on melt treatment of LM13. However, change in morphology of primary silicon particles was not significant as for LM28. Heat treatment of both alloys caused spheroidization and better distribution of eutectic silicon crystals. Sharp-edged primary silicon particles were rounded off after the heat treatment of LM28. Scanning electron microscopy (SEM) of tensile fractured surfaces was carried out to study the influence of microstructure on fracture mode. Heat treatment of both alloys promotes dimple fracture. However, as-cast and melt-treated alloys show predominantly cleavage fracture.     

Al-Si合金变质元素及其交互作用

铸造Al-Si合金具有轻量化、流动性好、气密性好、收缩率小和热膨胀系数低等优点,已成为铸造业中最受重视的结构材料之一。铸造Al-Si合金的力学性能主要取决于组织中的α-Al相、共晶硅、初生硅、金属间化合物、缺陷以及它们的形态、尺寸和分布,其中硅相和富Fe相的形貌、尺寸及分布对合金性能的影响尤为显著。未变质的Al-Si合金中针片状共晶硅和针状β-Fe相严重割裂基体,粗大块状初生硅和针片状共晶硅尖端和棱角部位产生应力集中,导致合金的性能尤其是塑性、强度和耐磨性显著降低。此外,硬脆的粗大初生硅还会加快机加工刀具的磨损,加工后零部件的表面光洁度也较差,无法满足实际生产的需要。快速凝固、电磁搅拌、超声处理、机械振动等特殊工艺技术虽然可以在一定程度上改善铸造铝硅合金的微观组织和性能,但是都需要专门的设备和特殊的条件,使其应用受到限制。变质处理不需要任何特殊设备,只需添加少量变质元素,就可以实现对其中α-Al相、共晶硅、富Fe相、细化初生硅等的有效调控,具有成本低、方法简单、效果显著等特点,已成为改善Al-Si合金组织、提高性能最有效的途径。然而,各变质元素的变质机理及它们之间的交互作用极其复杂,如何充分发挥各变质元素及它们之间积极的交互作用是当前的研究热点。近年来对单一变质元素的变质作用机理和效果的研究进展迅速,先后发现了Na、Sr、Sb、P、Ti、Mn和RE等都对铸造铝硅合金有一定的变质作用,并且对它们的变质时效性以及经济性都有了充分的认识。与此同时,也有许多研究者开始关注多元素的交互变质作用并在Sr-X、P-X、Mn-X、Ti-X等二元交互变质方面取得了重要的成果,使变质技术更加经济、有效和灵活。本文综述了铸造Al-Si合金常用单一变质元素的特点、变质作用机理和局限性,系统归纳了Sr、P、Ti、Mn和RE与其他元素间的交互作用规律,筛选出具有协同变质作用的二元/多元变质元素交互作用对,以期为深入探究二元/多元变质元素交互作用的机理,开发更高效、多样、绿色的复合变质剂及变质处理方法提供参考。     

Calculating GaAs semiconductor nanoneedle size distribution

The temporal evolution of an ensemble of semiconductor (GaAs) nanoneedles (NNs) growing on a lattice-mismatched substrate (silicon, sapphire) has been theoretically analyzed assuming the validity of the Gaussian law of nucleation and constancy of the NN shape during growth. The NN size distribution function is determined for various moments of time. The results of analysis can be used for optimization of growth methods aimed at obtaining NN ensembles with preset morphology.     

Three‐dimensional morphology of eutectic silicon in as‐cast Al‐20 wt% Si alloy with ultrasonic treatment

Three‐dimensional morphology of eutectic silicon in as‐cast Al‐20 wt% Si alloys with ultrasonic treatment above liquidus has been investigated in this paper. The results show that ultrasonic treatment above liquidus could not refine the primary silicon phase very well, but is capable of modifying the morphology of eutectic silicon. The fracture of eutectic silicon occurred resulting in both huge reduction of silicon grain sizes and changes of morphology from large plate‐like to interconnected thin flake and coral‐like. The evolution mechanisms of the eutectic silicon morphology in Al‐20 wt% Si alloys with ultrasonic treatment were also preliminarily discussed.     

Refinement of Cast Microstructure of Hypereutectic Al-Si Alloys Through the Addition of Rare Earth Metals

Microstructural observation and thermal analysis of Al-21 wt % Si alloys with different rare earth metals were performed to examine the effect of rare earth metal on the refinement of primary silicon phase. Simultaneous refinement of both primary and eutectic silicon morphology is achieved with the addition of rare earth and its effect increases with the amount of rare earth addition and cooling rate. Depression of 12–17 °C in primary reaction temperature and 2–7 °C in eutectic temperature is measured with the addition of rare earth. Rare earth bearing compounds were not believed to act as a nucleation agent of primary silicon phase. Some rare earth bearing compounds determined to AlCe were around primary silicon in the matrix. The twin density of eutectic silicon remains same regardless of the addition of rare earth. The refinement of silicon in rare earth treated hypereutectic Al-Si alloys is supposed to be due to the suppression of the nucleation temperature of silicon phase.