探析熔体过热处理对亚共晶Al-Si合金凝固特性和组织的影响

文章将亚共晶Al-Si合金为研究对象,分析熔体过热处理对其凝固特性与组织的影响,在实验室配制Al-Si合金,对其进行熔体过热处理实验,分析不同实验条件下,Al-Si合金的凝固组织变化。     

快速凝固铝硅合金的制备、组织特征及断裂行为

快速凝固Al-Si合金是一种高性能结构材料,目前主要通过快速凝固/粉末冶金(RS/PM)和喷射沉积(SF)两种方法进行制备;此类合金具有超细化显微组织、成分均匀分布、非平衡亚稳相和过饱和固溶体及高密度位错等组织特征;其断裂方式主要呈脆性断裂。本文主要对上述内容进行综合评述     

稀土在Al-Si活塞合金中的作用及其机理

Al-Si合金常作为一种高质量活塞合金广泛应用于内燃机生产中,在Al-Si活塞合金中添加稀土元素可以明显改善合金的机械力学性能和铸造加工性能。本文概述了稀土在Al-Si活塞合金中的作用。通过对大量试验研究结果的分析,着重论述了稀土对Al-Si活塞合金的细化变质、脱氧、除气和除Fe的作用及其机理,对进一步开展稀土在铝硅合金中的细化变质等应用研究具有广泛的理论和现实意义。     

冷却速度对多元铝硅铸造合金组织与性能的影响

近共晶多元Al-Si合金在汽车、航空、军事领域有广阔的应用前景,通过改变合金冷却速度可以有效改善合金的显微组织。本文通过快速凝固甩带和水冷铜模铸造技术获得Al-11.5Si-4Cu-2.7Ni-Mg-0.45Fe合金,采用金相显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)等分析测试手段,研究了两种冷却速度对合金微观组织和显微硬度的影响。结果表明,甩带样品的硬度相对水冷铜模样品提高32.22%。此外,水冷铜模铸造使合金显微组织中初生硅尺寸相对常规金属型铸造明显减小;快速凝固甩带样品元素分布较水冷铜模样品更加均匀,甩带样品的微观组织由等轴状α-Al枝晶及少量非晶相组成,不存在明显的凝固析出AlCuNi相,尤其是没有明显Si相的析出。而且,快速凝固甩带试样中Fe元素含量在不同的位置差距比较大,而Mg,Ni,Cu元素的含量差距不大,这与不同金属元素的晶格结构有关。快速凝固甩带的铝相各峰的极值位置相对于水冷铜模向左偏移,即衍射发生小角度偏移,这与合金元素的过固溶有关。     

快速凝固Cu-30,35％Fe合金微观组织的分析研究

采用快速凝固技术制备了Cu-Fe合金。使用VHX-600超景深显微镜对Cu-Fe合金快速凝固组织进行观察,且与其普通凝固条件下的微观组织作对比,研究了快速凝固对铜铁合金的凝固过程和微观组织的影响。结果表明:快速凝固可以产生很大的过冷度,Cu-Fe合金与Cu-Co合金一样在快速凝固过程中发生液相分解。     

稀土Nd对活塞用Al-Si合金显微组织和力学性能的影响

研究了Nd含量对活塞用Al-Si合金的组织演变和力学性能的影响。通过金相显微镜(OM)、扫描电子显微镜(SEM)分析了Nd对该合金凝固过程中析出相的形貌和分布的影响。并对其力学性能进行了测试研究。结果表明:当Nd含量≤0.3%时,随着Nd含量的增加,α-Al基体得以细化。在Nd含量0.3%时,初生硅的等积圆直径较未添加Nd时减小了73%,当Nd含量增加至0.8%及以上时,合金中出现了富稀土相,其力学性能显著降低。Nd含量为0.3%的Al-Si合金的350℃抗拉强度较未添加Nd的Al-Si合金提高了29.8%。由于Nd元素聚集在AlCuNi相周围,造成了成分过冷,抑制了AlCuNi相的长大,AlCuNi相由粗大的骨骼状转变为细小的棒状。     

高能球磨稀土高硅铝合金粉末性能表征

对快速凝固法制备得到的Al-20Si-0.35RE合金进行不同时间的高能球磨, 然后对球磨后的粉末进行多次热压变形, 采用XRD, ESEM以及TEM等表征变形前后合金粉末的显微组织, 并对变形后合金的导电性能进行了研究. 研究发现快速凝固Al-20Si-0.35RE合金粉末的显微组织主要由细小的Al-Si固溶体(0.3～0.5 μm)、初晶硅、稀土铝硅化合物(0.16～0.3 μm)组成; 随着球磨时间延长, 颗粒粒径显著减小; 经过多次热压变形后合金晶粒显著细化, 晶格畸变减小, 位错钉扎稀土化合物, 形成类似表面渗流效应, 合金导电率提高至70%IACS.     

偏析和缩松均少的铸造Al-Cu合金的制备

正欧洲专利US2013068411本专利涉及一种铸造用Al-Cu合金,该合金具有比Al-Si合金较高的强度,但是铸造流动性较差,而且合金元素的偏析较重和枝晶间的缩松较多。为了减少或避免这种现象的产生,在该合金中加入一些高度分散细小的又硬又脆又不溶的颗粒,充填于枝晶的间隙,这样既不降低合金的韧性,又能改变Al-Cu合金的凝固状态和补缩条件,从而较好地解决了合金的偏析和缩     

快速凝固AB_5型贮氢合金显微组织、吸氢及电化学性能

对AB5型快速凝固贮氢合金与其铸态合金在显微组织、吸氢性能、电化学性能等方面进行了对比研究。发现快速凝固合金有细小的 1～ 5 μm胞状、等轴状微晶组织 ;快速凝固合金的P C T曲线平台比铸态合金平缓 ,且压力低 ;快速凝固合金容量及活化性能低于铸态合金 ,但经退火后可以部分改善 ;快速凝固合金电极循环寿命明显优于铸态合金 ,主要是因为合金的晶粒细小可以抑制合金的微粉化和氧化。     

Al—3B中间合金的加工量对亚共晶Al—Si合金晶粒细化的影响

研究了Al-3B中间合金不同的加入量对亚共晶Al-Si合金晶粒尺寸的影响。该中间合金对所研究全部范围内的Al-Si合金都具有一定的细化效果,但在不同的含硅量下其细化能力并不相同,同时证实对未经细化处理的亚共晶Al-Si合金而言,在含硅量约3%（质量分数,下同）时合金具有最小的晶粒尺寸。随着Al-3B中间合金加入量的提高,出现最小晶粒尺寸的合成成分向高硅方向移动,当加入量达到1%时,在含硅量为6%的Al-Si合金中出现最小的晶粒尺寸。     

Dendritic Arm Spacing Affecting Mechanical Properties and Wear Behavior of Al-Sn and Al-Si Alloys Directionally Solidified under Unsteady-State Conditions

Alloys of Al-Sn and Al-Si are widely used in tribological applications such as cylinder liners and journal bearings. Studies of the influence of the as-cast microstructures of these alloys on the final mechanical properties and wear resistance can be very useful for planning solidification conditions in order to permit a desired level of final properties to be achieved. The aim of the present study was to contribute to a better understanding about the relationship between the scale of the dendritic network and the corresponding mechanical properties and wear behavior. The Al-Sn (15 and 20 wt pct Sn) and Al-Si (3 and 5 wt pct Si) alloys were directionally solidified under unsteady-state heat flow conditions in water-cooled molds in order to permit samples with a wide range of dendritic spacings to be obtained. These samples were subjected to tensile and wear tests, and experimental quantitative expressions correlating the ultimate tensile strength (UTS), yield tensile strength, elongation, and wear volume to the primary dendritic arm spacing (DAS) have been determined. The wear resistance was shown to be significantly affected by the scale of primary dendrite arm spacing. For Al-Si alloys, the refinement of the dendritic array improved the wear resistance, while for the Al-Sn alloys, an opposite effect was observed, i.e., the increase in primary dendrite arm spacing improved the wear resistance. The effect of inverse segregation, which is observed for Al-Sn alloys, on the wear resistance is also discussed.     

Study on Improving Solidification Structure of Rare Earth Al-Si Alloys with Electropulse Acting on Liquid Alloy

Electropulse modification (EPM) process, a new physical field method for improving the solidification structure of metals was introduced.Different from other research, EPM is only acting pulse current on melt under liquid state.The solidification structure of Al-Si alloys, A1-Cu alloys,cast iron and steel can be modified obviously with this method: the solidification structure of ZL101 alloy presented the Na and Sr modification and the mechanical properties were enhanced; a large number of primary silicon appeared in the microstructure of ZL109 alloy; the equiaxed grain zone was expanded and the grains were fined in Al-5.0wt% Cu alloy; the graphitization took place in solidification process of molten cast iron; the grain sizes of solidification structure of T8 steel were reduced significantly and the shape of steel pearlites also changed; the equiaxed grain zone increased to 88% from original untreated 19%, the equiaxed grains were fined and the intercrystalline crack was avoided in concasting billet by continuously treating liquid electrical sheet steel in tundish.Effects of rare earths on casting Al-Si alloys were also summarized.The method of modifying the solidification structure of rare earth Al-Si alloys with EPM in producing the alloys was proposed.     

Effect of erbium on properties and microstructure of Al-Si eutectic alloy

Eutectic Al-12.6 wt.%Si alloys with various contents of the rare earth dement Er were prepared by the conventional casting technique.The effect of Er on the microstructure and properties of the eutectic Al-Si alloys was investigated using optical microscopy,scanning electron microscopy as well as the friction and wear tests.It was found that the addition of Er obviously improved the anti-wear properties,and reduced the friction coefficient of the alloys.The appropriate addition of Er would change the size and shape of the eutectic silicon,and thereby refine the microstructure of the Al-Si alloys.The refinement mechanism was also discussed.     

铝硅焊片对异种铝合金电子束焊接焊缝组织性能的影响

采用电子束焊接技术,研究厚度为20 mm的AlCu0.5,AlSiCu,AlSi1三种高纯铝合金分别与6061铝合金的焊接效果。通过添加铝硅焊片来改善异种铝合金焊接的组织性能。对焊缝区域组织的分析表明,不同焊片添加量改变铝合金焊缝中的Si含量,从而对焊接的裂纹敏感性有显著的影响。当焊缝中Si含量在1%左右时容易产生裂纹缺陷,随着焊缝中Si含量的增高,焊缝中的裂纹逐渐减小,直至没有裂纹缺陷的产生。焊缝的硬度也随焊缝中Si含量的增高而变大。针对不同的高纯铝合金与6061的焊接,通过添加合适的铝硅焊片,能获取组织性能优异的焊缝。     

Influence of Mg on Grain Refinement of Near Eutectic Al-Si Alloys

Although the grain-refinement practice is well established for wrought Al alloys, in the case of foundry alloys such as near eutectic Al-Si alloys, the underlying mechanisms and the use of grain refiners need better understanding. Conventional grain refiners such as Al-5Ti-1B are not effective in grain refining the Al-Si alloys due to the poisoning effect of Si. In this work, we report the results of a newly developed grain refiner, which can effectively grain refine as well as modify eutectic and primary Si in near eutectic Al-Si alloys. Among the material choices, the grain refining response with Al-1Ti-3B master alloy is found to be superior compared to the conventional Al-5Ti-1B master alloy. It was also found that magnesium additions of 0.2 wt pct along with the Al-1Ti-3B master alloy further enhance the near eutectic Al-Si alloy’s grain refining efficiency, thus leading to improved bulk mechanical properties. We have found that magnesium essentially scavenges the oxygen present on the surface of nucleant particles, improves wettability, and reduces the agglomeration tendency of boride particles, thereby enhancing grain refining efficiency. It allows the nucleant particles to act as potent and active nucleation sites even at levels as low as 0.2 pct in the Al-1Ti-3B master alloy.     

Effects of microstructure on the erosion of Al-Si alloys ny solid particles

The effects of microstructure on the erosion of Al-Si alloys by 40 μm Al₂O₃ particles were investigated. The impact angle dependence of the erosion rate of Al and the Al-Si alloys exhibited the ductile signature, whereas that for pure Si showed the brittle signature. The eroded surface of pure Al was characterized by craters, lips, overlaps and folds, and platelets; that for pure Si exhibited complex radial and lateral cracking at the impact site. At shallow impact angles these features were elongated in the direction of the tangential component of the velocity in both materials. The measured erosion rates of the Al-Si alloys were found to be in accord with an inverse rule of mixtures based on pure Al and pure Si; better agreement was, however, obtained if pure Al and the eutectic were taken as the two constituents for the hypoeutectic alloys, and pure Si and the eutectic for the hypereutectic alloys. The microstructure size had two effects: (a) scaling with respect to the impact damage zone size and (b) an influence on the physical and mechanical properties which govern material removal. The present results are considered in terms of current models for the erosion of ductile and brittle materials.     

Al—10Ce中间合金对ZL102共晶Al—Si合金的变质研究

分析研究了Al—10Ce中间合金对ZL102共晶铝硅合金的变质处理效果。结果表明,Al—10Ce中间合金用量、熔体中的杂质以及冷却速度对变质效果的影响很大,Al-10Ce中间合金用量为0．9％左右时达到最佳变质效果,提高Al—Si的纯度可以获得变质组织,冷却速度超过70℃／min时才具有明显的变质效果。     

Effects of microstructure on the erosion

The effects of microstructure on the erosion of Al-Si alloys by 40 μm Al₂O₃ particles were investigated. The impact angle dependence of the erosion rate of Al and the Al-Si alloys exhibited the ductile signature, whereas that for pure Si showed the brittle signature. The eroded surface of pure Al was characterized by craters, lips, overlaps and folds, and platelets; that for pure Si exhibited complex radial and lateral cracking at the impact site. At shallow impact angles these features were elongated in the direction of the tangential component of the velocity in both materials. The measured erosion rates of the Al-Si alloys were found to be in accord with an inverse rule of mixtures based on pure Al and pure Si; better agreement was, however, obtained if pure Al and the eutectic were taken as the two constituents for the hypoeutectic alloys, and pure Si and the eutectic for the hypereutectic alloys. The microstructure size had two effects: (a) scaling with respect to the impact damage zone size and (b) an influence on the physical and mechanical properties which govern material removal. The present results are considered in terms of current models for the erosion of ductile and brittle materials. Formerly with the Department of Materials Engineering, Formerly with the Department of Materials Engineering,     

Effect of the Delay in Time Between Cooling and Aging in Heat-Treated Cast Aluminum Alloys

The mechanical properties of cast aluminum alloys can be affected by the delay in time involved between the stages of rapid cooling after solubilization (quenching) and aging. This effect was studied on samples from three different Al-Si alloys that were cast with a wide range of microstructures. It was found that the parameter that exerts the highest influence on the mechanical properties is the degree of microstructural refining, which is referred to dendrite arm spacing, as a finer structure enhances the strength and ductility. It was found that the yield strength and total elongation, and to a lesser extend the ultimate tensile strength, are affected by the delay in time. The material that was treated to the peak-aged condition was found to be more susceptible to the reduction in mechanical properties with the increase in the delay in time.