Bi和Sr改性Al-7Si-0.4Mg合金显微组织的影响(英文)

研究单独添加Bi和联合添加Bi与Sr在不同凝固条件下对Al-7Si-0.4Mg合金中共晶硅结构的影响。结果表明:添加Bi对共晶硅有细化作用,其细化能力随着Bi质量分数(在<0.5%范围内)的增加而增强。当Bi添加到Sr改性的合金中时,为了得到充分的共晶硅改性,较高的Sr/Bi质量比(至少0.45)是必要的。     

铸造Al-Si合金中Sr与B的交互作用

采用X射线能谱仪和X—ray Mapping对反应产物进行分析，由Al-Si合金中不同Sr，B含量时枝晶α和共晶Si形态与大小的变化，考察了Sr与B的交互作用。研究发现：Al—lB中间合金在经Sr变质处理的近共晶Al-Si合金中具有强的枝晶细化能力，而Sr的存在对B的枝晶细化效果起一定的促进作用；但当合金中Sr和B含量较高时存在互毒化现象，这是由于Sr与B摩尔比接近3：4的未知化合物形成时消耗了熔体中大量的Sr和B。Sr—B化合物的发现为Sr，B间互毒化机理提供了直接依据。     

United modification of Al-24Si alloy by Al-P and Al-Ti-C master alloys

The modification effect of a new type of Al-P master alloy on Al-24Si alloys was investigated.It is found that excellent modification effect can be obtained by the addition of this new type of Al-P master alloy into Al-24Si melt and the average primary Si grain size is decreased below 47μm from original 225μm.It is also found that the TiC particles in the melt coming from A18Ti2C can improve the modification ffect of the Al-P master alloy.When the content of TiC particles in the Al-24Si melt is 0.03%.the improvement reaches the maximum and keeps steady with increasing content of TiC particles.Modification effect occurs at 50 min after addition of the Al-P master alloy and TiC particles,and keeps stable with prolonging holding time.     

Effect of strontium on columnar growth of dendritic α phase in near-eutectic Al-11.6%Si alloys

For Al-11.6 % Si alloy, the influence of the addition of Sr on the morphology of the dendrite α phase was investigated, and the characteristic parameters of the dendrite α phase, the primary dendrite spacing and the secondary dendrite arm spacing, were also measured. The addition of strontium promotes the columnar dendrite growth and leads to a decrease of both the primary dendrite spacing and secondary dendrite arm spacing with the increase of the content of strontium in the modified near-eutectic Al-Si alloys. It is thought that the addition of Sr leads to a reduction of the solid-liquid interfacial energy of the dendrite α phase, consequently resulting in a decrease of the growth undercooling of dendrite tips. And hence, the nucleation of the equiaxed grains in the liquid in front of the columnar dendrite tips is restrained, thus the addition of strontium in Al-Si alloys promotes the growth of the columnar dendrites. The reduction of the solid-liquid interfacial energy also leads to the decreases in the primary dendrite spacing and the secondary dendrite arm spacing.     

Effect of Iron Impurity and a Cd Trace Addition on the Delayed Ageing of Al-7Si-0.3 Mg Casting Alloy

Abstract

Iron in aluminium alloys is considered to be an impurity. It forms intermetallic compounds with Al and elements Si and Mg; these coarse intermetallic compounds impair the mechanical properties. An increase in hardness and decrease in UTS, YS, and ductility was observed with an increase in Fe content in the range 0.2 to 0.8% in an Al-7Si-0.3Mg Alloy. Further analysis showed higher hardening rate of the alloy at 0.8% Fe compared to 0.2% Fe with the tensile flow curves. Studies were carried out on the effect of chemical composition (Mg, Fe), solidification rate, heat treatment (delayed ageing with Cd trace addition) on microstructure and mechanical properties of the alloy. Chill castings were found to possess higher mechanical properties than sand castings.     

Effects of individual and combined additions of phosphorus, boron and cerium on primary and eutectic silicon in an Al-30Si alloy

The modification of silicon in an Al-30Si alloy was studied using optical microscopy, electron probe micro-analysis, transmission electron microscopy and differential scanning calorimetry. It is found that phosphorus master alloys combined with boron master alloys have good modification effect on primary silicon but no evident modification effect on eutectic silicon, while boron combined with cerium has good modification effect on eutectic silicon. The results of differential scanning calorimetry show that phosphorus, boron or cerium addition and their combined addition have different undercooling effects on eutectic silicon. Many scholars thought that AlP particles were the nuclei of eutectic silicon when phosphorus was enough in the alloy. Our results show that β-(Al,Si,Fe) can still be the nucleus of plate-like eutectic silicon while AlP is the nucleus of primary silicon when there is enough phosphorus in the melt. In addition, the mechanism about the modification was also discussed.     

Effect of strontium on crystallization of Mg2Si phase in Al—Si—Mg casting alloys

Otical microscope and SEM were used to observe the changes of the microstructure of Al-11.6%Si-0.4% Mg alloys with varying strontium additions and the effect of strontium on the crystallization of Mg2Si phase was discussed.It is found that Mg2Si phase nucleastes on the the surfaces of the eutectic silicon flakes in the unfully modified alloys,growing as meshwork or bamboo-shoot shape,however,very few and fine Mg2Si particles phase are isolated at the boundaries of the eurectic cells in the fully modified alloys.Strontium has an important influence on the crystallization of Mg2Si phase in the Al-Si-Mg casting alloys and it is thought to be related to the increase of the amunt of dendritic αphase and the modifying degree of eutectic silicon phase.     

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。     

变质处理对Al-11.7%Si合金耐蚀性的影响

对未变质、Na变质和Sr变质Al-11.7%Si合金在4%硫酸水溶液中进行了失重腐蚀试验,分别用扫描电子显微镜和光学显微镜观察试样表面腐蚀形貌和纵深腐蚀状况。结果表明,在强酸环境中未变质合金的耐蚀性最好,Sr变质合金次之,Na变质合金最差。浸蚀360h之前,三种合金的腐蚀行为都表现为均匀腐蚀。360h后,点蚀成为变质合金腐蚀行为的主要特征。Sr变质合金蚀孔深、横向腐蚀缝不发达。而Na变质合金蚀孔略浅,但横向腐蚀缝相当发达。480h后Na变质合金中横向腐蚀缝趋于相互贯通导致剥蚀发生。Na变质合金与Sr变质合金腐蚀行为的差异可能与合金组织中枝晶!的排列位向有关。     

铸造Al-Si合金Sr变质处理过程中共晶硅形态的渐变行为

通过光学显微镜和SEM考察了共晶硅形态与大小随Al-11.6%Si合金中Sr量的变化.研究发现共晶硅从片状转变成纤维状的过程并不是突变的,而是一个渐变过程,共晶硅的形态存在一个介于二者之间的中间态,具有明显的弯折与分叉,同时也具有纤维硅的特征.随着合金中Sr量的增加,共晶过冷度增大,同时孪晶边界能降低,使得硅相产生弯折、分叉,硅相形态不断向纤维化转变.     

Sr,B添加对Al-15.5%Si合金中共晶团尺寸的影响

考察了Sr,B及Sr＋B联合作用对Al-15．5％Si（质量分数）合金中共晶团尺寸大小的影响．实验结果表明,随合金中Sr量增加,共晶团尺寸呈减少的趋势,冷却速度对共晶团的影响也很显著;在Sr变质的合金中加入B,共晶团尺寸先显著下降,随B量增加降低幅度趋于平缓;在未变质的Al-15.5％Si合金中单独加B,共晶硅由粗大的片状变为细长的层片状,层片间距明显降低．分析认为,合金中加入Sr,导致共晶过冷度增大,因而共晶团形核驱动力增大促使共晶团细化;合金中加入B,增加了共晶团有效形核基底的数量促使共晶团显著细化．     

Three-dimensional characteristics of Fe-rich intermetallics in gravity-cast Al-6Si alloys

Fe-rich intermetallics, especially β-Fe phase, usually forming in the microstructure of cast aluminum alloys, are very detrimental to mechanical properties. In the present work, the effects of Fe content on phase transformation and microstructures were analyzed using a 3D X-ray microscope. Based on the high-resolution 3D X-ray computed tomography, the 3D characteristics of Fe-rich intermetallics and micropores in the gravity-cast Al-6Si alloys with different Fe contents were investigated. In addition, the effect of intermetallics on the microporosity was discussed. The results show that with increasing the Fe content from 0.10wt.% to 0.60wt.%, the volume fraction of Fe-rich intermetallics and the volume of the largest size Fe-rich intermetallic increased, and the 3D morphology of intermetallics changed from fine flake to network aggregation. As the Fe contents increased, the shrinkage pores were characterized, which were rather complex due to the micropores promoted by the intermetallics interactions.     

变质处理和快速凝固作用下的Al-7Si合金的Si相形貌(英文)

通过快速凝固和变质处理的综合作用,在铸态铝硅亚共晶合金中原位获得了纤维硅相组织。讨论了各种因素对硅相形态及其演化的影响,重点讨论变质处理对合金组织的改性机制,同时还详细讨论了冷却速率对硅相形态演化的影响。此外,本研究提供了一种制造直纤维增强铝基复合材料的新方法。     

Thermal Properties of Al-50%Si Alloys

AS FOR Al-Si alloy,this alloy with the characteristicsuch as excellent in a low coefficient of thermalexpansion(CTE),high-heat-conductivity,and wearresistance is used for the piston material of the engine,the heat radiation material,and electronic application1'2.The CTE of the Al-Si alloy decreases further withincreasing Si content because the CTE of Si is low3.The strength and wear resistance of Al-Si alloydecrease with increasing Si content because eutectic Siis coarse grain size an…     

微合金化对Al-7%Si合金组织与时效行为的影响

采用硬度测量、金相观察,并结合差示扫描量热分析（DSC）等方法,研究了Mg、Ti、Zr、Sn等元素微合金化对Al-7%Si合金的显微组织、性能和时效行为的影响.研究发现,微合金化可以显著改变Al-Si显微组织的形貌,使合金的组织均匀、细小.微合金化后Al-Si合金的铸态硬度提高,但在T6处理后,添加Sn使得合金硬度降低;Al-7Si-0.55Mg合金时效的最佳工艺为175 ℃保温160～210 min,此时起增强作用的可能是GPⅡ区和β＇相.     

Semisolid casting with ultrasonically melt-treated billets of Al-7mass%Si alloys

The demand for high performance cast aluminum alloy components is often disturbed by increasing impurity elements,such as iron accumulated from recycled scraps.It is strongly required that coarse plate-like iron compound of β-Al5FeSi turns into harmless form without the need for applying refining additives or expensive virgin ingots.The microstructural modification of Al-7mass%Si alloy billets with different iron contents was examined by applying ultrasonic vibration during the solidification.Ultrasonically melt-treated billets were thixocast right after induction heating up to the semisolid temperature of 583 oC,the microstructure and tensile properties were evaluated in the thixocast components.Globular primary α-Al is required to fill up a thin cavity in thixocasting,so that the microstructural modification by ultrasonic melt-treatment was firstly confirmed in the billets.With ultrasonic melt-treatment in the temperature range of 630 oC to 605 oC,the primary α-Al transforms itself from dendrite into fine globular in morphology.The coarse plate-like β-Al5FeSi compound becomes markedly finer compared with those in non-treated billets.Semisolid soaking up to 583 oC,does not appreciably affect the size of β-Al5FeSi compounds;however,it affects the solid primary α-Al morphology to be more globular,which is convenient for thixocasting.After thixocasting with preheated billets,eutectic silicon plates are extremely refined due to the rapid solidification arising from low casting temperature.The tensile strength of thixocast samples with different iron contents does not change much even at 2mass% of iron,when thixocast with ultrasonically melt-treated billets.However,thixocast Al-7mass%Si-2mass%Fe alloy with non-treated billets exhibits an inferior strength of 80MPa,compared with 180MPa with ultrasonically melt-treated billets.The elongation is also improved by about a factor of two in thixocastings with ultrasonically melt-treated billets for all iron contents of Al-7mass%Si alloys,for example,the elongation of 11% in thixocast of Al-7mass%Si-0.5mass%Fe alloy with ultrasonically melt-treated billets,5% in that with non-treated billets.     

Influences of complex modification of P and RE on microstructure and mechanical properties of hypereutectic Al-20Si alloy

P and RE complex modification of hypereutectic A1-Si alloys was conducted. The influences of P, RE content on the microstructure and mechanical properties of alloys were investigated. The complex modifications of P and RE make the coarse block primary silicon obviously refined and the large needle eutectic silicon modified to the fine fibrous or lamella ones. P mainly refines the primary silicon, but excess P is unfavorable to the refinement of primary silicon. RE can well refine the primary and eutectic silicon, but its modification effect on the eutectic silicon is more obvious. P can repress the modification of RE on the eutectic silicon The alloys with the additions of 0.08% P and 0.60% RE have the optimal microstructure and the highest mechanical properties. Compared with the unmodified alloy, the primary silicon of alloys can be refined from 66.4 μm to 23.3μm and the eutectic silicon can be refined from 8.3 μm to 5.2μm. The tensile strength is improved from 256 MPa to 306 MPa and the elongation is improved from 0.35% to 0.48%.     

Modification mechanism of cerium on the Al-18Si alloy

The effect of the rare earth cerium （Ce） on the hypereutectic Al-Si alloy under different casting states have been studied by optical microscope and quantitative image analysis. It is found that the size and the quantity of primary silicon in castings decrease with the increase of added Ce in the melt. Meanwhile primary silicon changes from branched shape to fine facetted shape. Although the modification on eutectic silicon in castings also improves with the increase of added Ce in the melt, the effect of modification on eutectic silicon away from primary silicon is more obvious than that on eutectic silicon close to primary silicon. The modification mechanism was analyzed in detail by means of scanning electron microscope equipped with energy dispersive analysis of X-ray and thermodynamics analysis, which included the analysis on the change in standard Gibbs energy of reaction and reaction equilibrium.     

Effects of ZnS modification on primary Si in hypereutectic Al-Si alloy

A new modifying agent, ZnS, was used as a refiner to modify primary silicon in hypereutectic AlSi alloy. The factors affecting the modification results, including addition level of ZnS and holding time, were investigated. The results showed that the average size of the most effectively modified primary silicon was 28.5 μm when the ZnS mixed powder addition was 0.15 wt.% with a holding time of 10 min. More important, the average size of primary silicon could remain below 40 μm despite the holding time extending to 120 min, which means ZnS is a promising modifying agent of primarySi in industrial applications.     

铸造Al-Si合金中Sr与B间反应产物的研究

通过观察不同Sr,B含量时Al-Si合金中枝晶α和共晶Si形态与大小的变化，考察了Sr,B间的交互作用，采用X射线能谱仪对反应产物进行了分析。研究表明反应产物呈现两种不同类型：当Sr含量在0.025-0.030,B含量在0.028-0.036（质量分数，％）范围内时，二者间交互作用形成细小的SrB6化合物颗粒相，数量很少，存在于枝晶α中心；但当合金中Sr和B含量高于此范围时，形成Sr,B原子比接近3：4的Sr-B化合物，颗粒尺寸大、数量较多，且大多出现在共晶区。Sr-B化合物的形成消耗了大量的Sr和B,削弱了二元素的变质效果，导致了Sr,B间的互毒化行为。该化合物的形成为Sr,B间互毒化机理提供了直接证据。