浇注温度及变质工艺对初生硅形态的影响

介绍了过共晶铝硅合金的细化变质方法和进展以及对变质工艺的影响因素,分析了过共晶铝硅合金的主要性质,研究了磷变质时,变质温度、浇注温度等工艺参数对过共晶Al-Si合金初晶硅细化的影响。结果发现采用磷变质合金,变质后初晶硅组织分布均匀,平均晶粒尺寸约为35μm,810℃浇注时的铸造组织最佳。     

铝硅合金中共晶硅在固溶处理时的形态转变

通过金相和扫描电镜观察研究了铸造铝硅合金中的共晶硅在固溶热处理过程中的形态变化。结果表明,共晶硅的粒化过程与效果不仅与固溶温度和保温时间有关,而且由变质状态决定的硅相铸态结构对其也有重要影响,且变质共晶硅和未变质共晶硅在固溶处理后的三维形态有所不同。变质处理对硅相的粒化过程有明显的促进作用。     

熔体过热处理对过共晶Al-Si合金微观组织的影响

研究了熔体过热处理对于含12.6％、15％、18％和25％Si的过共晶铝硅合金组织形貌的影响.熔体过热处理温度范围600～1100℃,恒定冷却速度为3.5 K/s,利用CAZ-2MAY金相分析软件测试了初晶硅的粒子形貌、尺寸分布、初晶硅粒子的体积百分含量及形状因子.结果显示,随着熔体过热处理温度的升高,初晶硅粒子的微观组织形态发生变化,初晶硅粒子尺寸呈现持续减小的趋势,有明显的变质效果;初晶硅体积分数呈现小幅度的降低.     

变质工艺影响过共晶Al-Si合金初晶硅细化的研究

研究了磷变质时,变质剂、变质温度、变质时间、浇注温度等工艺参数对过共晶Al-Si合金初晶硅细化的影响。结果表明,上述工艺参数严重影响初晶硅的变质效果。当采用赤磷 铝粉 熔剂变质时,磷较易被吸收,变质后,合金中初晶硅含量较高。采用磷变质A390合金的最佳变质温度为800℃,变质后初晶硅组织分布均匀,平均晶粒尺寸约为13μm。高于此温度,初晶硅晶粒发生长大;低于此温度,初晶硅发生聚集。磷变质的最佳变质时间为20~30分钟。浇注时,800℃的铸造组织最佳,降低浇注温度,初晶硅晶粒严重聚集;升高浇注温度,晶粒变粗。     

铝硅合金变质机理的新发展和新观点（下）

铝硅合金变质机理的新发展和新观点（下）上海交通大学黄良余３铝硅共晶合金初晶硅及共晶硅晶体生长形态观察［２］通过引入特定晶面单晶籽晶，系统地观察了变质前后初晶硅的生长形态，发现变质剂既影响硅相的成长，同时减少了活性基底的数目，使晶胚“毒化”，也影响硅相...     

热处理和冷变形量对定膨胀合金4J32C线膨胀系数的影响

研究了不同热处理制度和不同冷变形量对定膨胀合金4J32C线膨胀系数的影响。结果表明,较小的冷变形量不会明显改变合金的线膨胀系数。随着固溶温度的升高,合金的线膨胀系数逐渐降低,在850 ℃时达到最低值,随后继续升高固溶温度,线膨胀系数略有增大。延长稳定化处理时间或提高稳定化处理温度,可适当增加合金的线膨胀系数。     

过共晶铝硅合金中初晶硅的变质机理探讨

过共晶铝硅合金中的初晶硅由于晶粒粗大并且有尖锐的棱角,严重的削弱了合金的机械性能,通常我们采用变质处理工艺来改善这一现象。目前很多研究表明硅元素变质的机理主要是孪晶凹谷机制。但是研究的对象都集中于亚共晶铝硅合金中的共晶硅。而对于含硅量高的过共晶铝硅合金．目前的研究内容是过共晶铝硅合金中的共晶硅或磷元素变质中的初晶硅的变质机理。对于钠盐变质的过共晶组织中初晶硅的变质机理未见报道．而恰恰初晶硅对过共晶组织性能的影响最深刻。因此实验研究对象锁定为钠盐变质的初晶硅变质机理。并且使用透射电子显微镜．通过标定透射衍射斑点研究硅相的变质机理。结果证明：变质元素的富集和择优吸附对共晶硅和初晶硅都是有效的,但实际上变质元素对两种硅相的变质效果是不同的。     

过共晶铝硅活塞合金的研制与生产

本文根据过共晶铝硅合金的特性,分析了Al-Si过共晶活塞合金的优化成份。研制了能用于批量生产的磷硫复合盐变质剂,该变质剂既能细化初晶硅又能细化共晶硅,而且变质有效时间长达3小时。合金性能超过国家标准(GB1148-82)要求。已用于批量生产。     

固溶时间对3种典型Al-Si二元合金组织与力学性能的影响

考察了固溶时间对3种典型Al-Si合金变质前后组织与力学性能的影响。结果表明：随着固溶时间的延长,变质前后的Al-Si合金抗拉强度逐渐降低,而伸长率有大幅度地提高;Al-12Si共晶合金抗拉强度及伸长率变化幅度最大;535℃固溶6h可获得综合性能较优的Al-Si合金;Sr的变质有助于固溶过程中共晶硅的粒化。     

不同变质剂对细晶铝锭共晶铝硅合金微观组织的影响

利用金相显微镜和扫描电镜研究了RE、P和P＋RE变质对细晶铝锭共晶铝硅合金组织中硅相的影响。结果表明,RE是共晶铝硅合金很好的变质剂,它可以球化共晶硅,当RE加入量为0．5％时,共晶硅相尺寸最小,达到2．7μm,圆形度为0．8;当RE加入量大于0．6％时,共晶硅相粗化,并且组织中出现了初晶硅。P变质对共晶铝硅合金组织有显著的影响,使组织在共晶成分出现初晶硅,对共晶硅没有变质作用。P＋RE联合变质时,P有毒化RE变质共晶硅的作用,合金组织中的共晶硅没有单独RE变质时球化的好;当P加入量为0．1％,RE加入量为0．4％时合金组织中初晶硅最小,为14．5μm,达到联合变质的最佳效果。     

Si、Cu和热处理工艺对Al-Si合金电导率的影响

通过电导率测量、金相观察、扫描电镜分析和X射线衍射分析,研究了Si含量、Cu含量和热处理工艺对Al-Si系铸造合金晶格常数和电性能的影响规律。结果表明:Si和Cu元素的添加会减小合金的电导率;当Si含量超过固溶极限后,Si含量的变化对晶格畸变程度影响不大,合金的电导率受Si相的体积百分数控制;而Cu在固溶极限内时,随其含量的增加,晶格畸变程度增大,合金的电导率可根据铝基体晶格常数的偏离量来评估;经过450℃,5 h+250,2 h热处理工艺,晶格畸变程度明显降低,合金的电导率有明显提高,增幅最高可达32%。     

Determination of latent heat and changes in solid fraction during solidification of Al-Si alloys by the CA-CCA method

Effects of Si content and the presence of various minor elements, e.g. Mg, Ti, Sr and P, on the latent heat of Al-Si alloys have been analysed by the CA-CCA method. The results indicate that the latent heat of Al-Si alloys increases with increasing Si content. For hypo-eutectic and eutectic alloys, Sr-modified and Ti-grain refined alloys release more latent heat than non-treated alloys. However, for hyper-eutectic alloys, the latent heat values are lower for P-refined and Ti-grain refined alloys than for non-treated alloys. In addition, the introduction of Mg into Al-Si alloys increases the latent heat. Linear and higher order regression formulae for fitting the latent heat with Si content have been obtained in this study. The results of the measured latent heat through both the CA-CCA method and the DTA method and the theoretical latent heat values calculated by the simple mixture rule have been compared.

Furthermore, the changes in solid fraction during solidification of Al-Si alloys with various compositions have also been determined by the CA-CCA method by taking into account the difference in latent heat between the Al and Si phases. Finally, the fluidity lengths of Al-Si(Mg) alloys have been related to latent heat, percent eutectic and superheat.     

Solidification behaviour of Al-7 %Si-Mg casting alloys

The effects of Mg content and cooling rate on the solidification behaviour of Al-7% Si-Mg(mass fraction)casting alloys have been investigated using differential scanning calorimetry, differential thermal analysis and microscopy. The Mg contents were selected as respectively 0.00%, 0.35% and 0. 70% (mass fraction). DTA curves of Al-7%Si-0.55%Mg(mass fraction) alloy at various cooling rates were accomplished and the alloy melt was cast in different cooling rates. The results indicate that increasing Mg content can lower the liquidus and binary Al-Si eutectic transformation temperatures. Large Fe-rich π-phases (AlsFeMg3Si6) are found in the 0.70% Mg alloys together with some small β-phases (Al5FeSi) ; in contrast, only β-phases are observed in the 0.35% Mg alloys. The test results of the Al-7%Si-0.55% Mg alloys identify that the liquidus and binary Al-Si eutectic transformation temperatures decrease, and the quantity of ternary Al-Si-Mg2 Si eutectic phase decreases as the cooling rate increases.     

Si含量和热处理制度对铸造Al-Si合金组织和性能的影响

为提高铸造Al-Si合金的力学性能,研究了Si含量和热处理制度对Al-Si合金组织和性能的影响。结果表明,Si含量、固溶冷却介质、固溶温度、时效时间、时效温度对Al-Si合金硬度的影响依次减小。Al-Si合金的最优Si含量及热处理制度为Si含量12%,480 ℃固溶120 min,盐溶液冷却及175 ℃时效90 min。随着Si含量的增加,Al-Si合金硬度和抗拉强度提升;但当Si含量超过共晶点时,方块状初生硅相析出,易形成应力集中使得合金强度降低,断裂方式由韧性断裂变为解理断裂。铸态Al-Si合金中共晶硅为长针状,经最优工艺热处理后,长针状转变为短棒或颗粒状,共晶硅更加分散,在拉伸过程中应力集中减少,位错运动阻力增加,使得Al-Si 合金的力学性能提高。     

Effect of phosphor addition on eutectic solidification and microstructure of an Al-13％Si alloy

As the refiner or modifier, the master alloys containing high concentration phosphor are widely used in preparing eutectic or hypereutectic Al-Si alloys. To study the effect of phosphor addition on the eutectic solidification and microstructure of the Al-13%Si alloy, an investigation has been undertaken by means of thermal analysis and micro/macro-structure observation. Results indicate that addition of phosphor in near eutectic Al-Si alloy promotes the nucleation of eutectic but has little refinement impact on primary Si particles as expected. Conversely, both primary Si particles and eutectic Si flakes become slightly coarser in P-rich alloys. The coarsening of eutectic Si flakes ties closely to the increased eutectic growth temperature with phosphor addition. The eutectic solidification of the alloy proceeds from the near mold zone towards the center, and it is also found that a few independent nucleation regions emerge in liquid at the solidification front due to the addition of phosphor.     

微合金化元素La对亚共晶Al-Si合金凝固组织与力学性能的影响

利用DTA、OM、SEM、TEM、EPMA以及拉伸实验等方法研究了在添加α-Al晶粒细化剂Al-Ti-B中间合金和共晶Si变质剂Sr条件下,微合金化元素La对亚共晶Al-Si合金凝固组织与力学性能的影响。结果表明:添加微量稀土La能进一步细化α-Al,变质共晶Si,显著提高合金的塑性。分析表明:微量La能降低α-Al晶核与TiB2的润湿角,减小α-Al的形核过冷度,促进α-Al的进一步细化;La能诱发交错孪晶的形成,增大共晶Si的孪晶密度,改变Si相的长大行为,进一步改变共晶Si的形貌。当La的添加量达到0.10%时,LaAlSi金属间化合物在凝固过程的共晶反应阶段形成,该化合物的形成将降低合金的塑性。     

Al-5Ti-1B和Al-P中间合金对Al-Si合金的联合变质作用

研究了Al-5Ti-1B和Al-P中间合金对Al-Si活塞合金组织和性能的影响。结果表明，加入0．2％Al-5Ti-1B中间合金能使经Al-P中间合金变质过的ZL109合金的共晶团和初晶硅进一步细化，抗拉强度也明显提高。随着Al-5Ti-1B加入的增加这种细化作用逐渐减小，当Al-5Ti-1B的加入量为2％时甚至使ZL109中的初晶硅变粗，抗拉强度也随之降低。     

改变共晶硅形态的研究

探讨了热处理规范对共晶硅形态的影响,结果表明,在高温下保温一定时间,在一定冷却条件下,共晶硅可以粒化;同时发现,随保温时间的延长,共晶硅会粗化、偏聚。对共晶硅形态的变化机理也作了初步探讨。     

Variation of microstructure of RE-containing AlSi20Cu2Ni1RE0.6 alloy with different cobalt contents

Cobalt is generally considered as the element that can promote the high-temperature mechanical properties of Al-Si alloys. In order to develop new hypereutectic Al-Si alloys that can be used at high temperature, the changes of microstructure of Al-20Si-2Cu-1Ni-0.6RE-xCo alloy with different contents of Co were studied in this paper. The results show that, under P-RE complex modification of the alloy melt, the content of Co varying from 0 to 1.5% had little influence on the refining effect of primary Si and modification effect of eutectic Si, but the amount of acicular RE-bearing Al-RE-Ni-Co-Si compounds gradually increased with the increase of Co content. In addition, Co could also modify the morphology of Fe-bearing phases, which solidified as particles instead of long needles. The addition of Co even has an adverse effect on the tensile strength of this RE-containing hypereutectic Al-Si alloy.     

Back Matter

The present work was performed on twenty-one alloys containing Al-11.5 wt% Si, with magnesium (Mg) in the range of 0.1–0.4 wt%, and copper (Cu) in the range of 1.0–3.0 wt%. Fluidity measurements and thermal analysis for each of these alloy melts were carried out. The alloys were cast in the form of tensile test bars. The test bars were solution heat treated at a temperature of ~500°C for 8h, then quenched in hot water (60°C), followed by artificial ageing at 155°C for 5 h, and then cooling in air. The effects of Mg and Cu additions on the tensile properties, depression in the Al-Si eutectic temperature, and microstructural characteristics (Si and Cu-phase particle characteristics and morphology) have been discussed in detail. The results show that the addition of Mg decreases the fluidity and the eutectic Si temperature. While addition of Cu also decreases the eutectic temperature, the fluidity, however, is increased. The presence of Mg and Cu decreases the modifying effect of Sr on the Si particles due to an increase in the solidification time, as well as the Sr, Mg, Cu interactions that occurs as a result of these additions. Mg additions in the range of 0.1–0.4 wt% increase YS (from 22% up to 94%) and UTS (from 7% up to 52%) and decrease the percent elongation (40%) depending on the Cu content of the alloy, i.e., the higher the Cu content, the lower the increase in strength. Addition of Cu has a similar effect on YS and UTS at alloy Mg levels of 0.1 wt% only, with no effect at higher Mg values, while elongation continuously decreases. The volume fraction of Al₂Cu phase increases by approximately 0.76% for every 1 wt% increase in Cu. This observation is important in the selection of the appropriate solution heat treatment regime in order to avoid incipient melting.