Overheating temperature of 7B04 high strength aluminum alloy

The microstructure and overheating characteristics of the direct chill semicontinuous casting ingot of 7B04 high strength aluminum alloy, and those after industrial homogenization treatment and multi-stage homogenization treatments, were studied by differential scanning calorimetry(DSC), optical microscopy(OM) and scanning electron microscopy with energy dispersive X-ray spectroscopy(SEM-EDX). The results show that the microstructure of direct chill semicontinuous casting ingot of the 7B04 alloy contains a large number of constituents in the form of dendritic networks that consist of nonequilibrium eutectic and Fe-containing phases. The nonequilibrium eutectic contains Al, Zn, Mg and Cu, and the Fe-containing phases include two kinds of phases, one containing Al, Fe, Mn and Cu, and the other having Al, Fe, Mn, Cr, Si and Cu. The melting point of the nonequilibrium eutectic is 478 ℃ for the casting ingot of the 7B04 alloy which is usually considered as its overheating temperature. During industrial homogenization treatment processing at 470 ℃, the nonequilibrium eutectic dissolves into the matrix of this alloy partly, and the remainder transforms into Al2CuMg phase that cannot be dissolved into the matrix at that temperature completely. The melting point of the Al2CuMg phase which can dissolve into the matrix completely by slow heating is about 490 ℃. The overheating temperature of this high strength aluminum alloy can rise to 500-520 ℃. By means of special multi-stage homogenization, the temperature of the homogenization treatment of the ingot of the 7B04 high strength aluminum alloy can reach 500 ℃ without overheating.     

高性能Al-Si-Cu-Ni-Mg活塞合金的相分析

采用高倍视频金相显徽镜（HRVM）和电子探针（EPMA）微区分析技术,观察了高性能Al-Si-Cu-Ni-Mg活塞合金的显微组织形貌,确认了合金中存在的构成相Mg2Si、Al3Ni、W相以及（CuNi）2Al3相。着重观察分析W相和Mg2SiN在热处理过程中的形态演变,发现多元共晶体中的W相固溶后由无序网格状呈现出典型的骨架状或者密堆状,Mg2Si相固溶处理后主要以固溶强化相融入到基体中。     

Effects of Solution Treatment on the Microstructure and Mechanical Properties of Al-16.9Si-4.5Cu-0.15Mg Alloy

In this paper, the microstructure and mechanical properties of Al-Si-Cu-Mg casting alloy under different solution conditions were investigated by optical metallographic and mechanical property test. The results show that the cast alloys were composed of α-Al, primary Si, eutectic Si, Al2Cu and Al7Cu2Fe phases. Three changes took place during solution treatment: Firstly, with the increase of solution temperature and the solution holding time extension, more and more Al2Cu phase was dissolved into the matrix; Secondly, with the increase of solution temperature and the solution holding time extension, morphology of eutectic Si, Al7Cu2Fe and other insoluble phases changed into more round; Thirdly, at the fixed solution temperature, if the solution time extended too long, it would cause grains, eutectic Si and other insoluble phases aggregated and coarsened. About mechanical properties, when the solution time was fixed, the hardness, tensile strength and the yield strength of the Al-Si-Cu-Mg alloy treated by T6 enhanced while the solution temperature increasing, and when the solution temperature was fixed, the ultimate tensile strength and the elongation of the Al-Si-Cu-Mg alloy treated by T6 increased at first and then decreased while the solution time increasing, but the hardness of the alloys affected less by the solution time.     

铜添加对近共晶Al-Si-xCu合金的微观组织和硬度的影响

研究铜含量对Al-Si-xCu（x=2%,3%,4%and5%）合金的微观组织和硬度的影响。不同铜含量的铝合金经熔炼后于690°C铸造成湿砂模并固化,于500°C保温7h进行固溶处理后对样品进行水冷。随后于190°C进行时效处理,分别保温5,10和15h,研究时效时间对基体硬度的影响。采用差热分析法,在冷却速度30K/min下确定平衡相的转变温度,并研究铜含量对四元共晶合金的形成和α（Al）＋Si熔点的影响。结果表明,随着铜含量的增加,发生析出硬化从而导致基体硬度增加,α（Al）＋Si的熔点降低,共晶相的含量增加。当铜含量超过2%时,生成熔点为507°C的四元共晶相。     

Three-dimensional rigid multiphase networks providing high-temperature strength to cast AlSi10Cu5Ni1-2 piston alloys

The three-dimensional (3-D) architecture of rigid multiphase networks present in AlSi10Cu5Ni1 and AlSi10Cu5Ni2 piston alloys in as-cast condition and after 4?h spheroidization treatment is characterized by synchrotron tomography in terms of the volume fraction of rigid phases, interconnectivity, contiguity and morphology. The architecture of both alloys consists of α-Al matrix and a rigid long-range 3-D network of Al(7)Cu(4)Ni, Al(4)Cu(2)Mg(8)Si(7), Al(2)Cu, Al(15)Si(2)(FeMn)(3) and AlSiFeNiCu aluminides and Si. The investigated architectural parameters of both alloys studied are correlated with room-temperature and high-temperature (300?°C) strengths as a function of solution treatment time. The AlSi10Cu5Ni1 and AlSi10Cu5Ni2 alloys behave like metal matrix composites with 16 and 20?vol.% reinforcement, respectively. Both alloys have similar strengths in the as-cast condition, but the AlSi10Cu5Ni2 is able to retain ～15% higher high temperature strength than the AlSi10Cu5Ni1 alloy after more than 4?h of spheroidization treatment. This is due to the preservation of the 3-D interconnectivity and the morphology of the rigid network, which is governed by the higher degree of contiguity between aluminides and Si.     

Al-Si合金中Si相的团粒化研究

利用金相和电子探针等手段研究了AC8C、ZL104和ZL109牌号的亚共晶及共晶Al-Si合金中共晶和初晶Si相的团粒化。结果表明，用Sr变质处理附以热处理手段相结合的方法可促使共晶Si相呈团粒状。并均匀分布干铝基体上，加入TiB2粒子可进一步促进共晶Si趋于圆滑，甚至使之团球化。使用杆状Al-P中间合金后，可使共晶Al-Si合金析出大量初晶Si，获得过共晶组织，并在一定条件下可促使初晶Si晶粒团粒化，提高活塞的金相等级。另外，在Si、Cu和Mg成分一定的条件下可形成一个球状复合相，为获得真正的球状Si相开辟了新思路。     

固溶处理AZ91-xCu合金的组织与腐蚀性能

以真空熔炼方法制备的AZ91-xCu(x=0、0.5、1、2)合金为研究对象,对其进行400 ℃保温12 h固溶处理,利用X射线衍射、扫描电镜、浸泡失重法及极化曲线测试等手段对合金的微观结构和腐蚀性能进行了研究。结果表明:铸态与固溶态AZ91-xCu合金基体主要由α-Mg与β-Mg₁₇Al₁₂相组成,Cu的添加使基体产生了Mg₂Cu、Cu₅Zn₈等相,其中固溶态AZ91-2Cu合金中出现了新相Al₂Cu;固溶处理时合金中的β-Mg₁₇Al₁₂相大量溶入基体,晶界明显,剩余第二相主要分布于晶界处,少量弥散分布于晶内;添加Cu与固溶处理均加快AZ91合金的腐蚀速率,其中固溶态AZ91-2Cu合金腐蚀速率最大。     

镍和锰对Al-Si-Cu-Mg合金凝固组织及时效硬化的影响

采用DSC差热分析及急冷试验方法并辅以微区成分分析 ,探讨了Ni和Mn对Al Si Cu Mg四元合金凝固组织、凝固过程及时效硬化特性的影响。Ni的加入量达 4%以上时 ,在组织中将形成初晶型Al Ni Cu三元化合物和共晶型Al Ni Cu三元化合物 ,若同时添加Mn ,则还会结晶出共晶型的Al Si Cu Ni Mn五元化合物 ;Ni和Mn的加入可以加快Al Si Cu Mg合金的时效硬化速度 ,同时又可推迟过时效现象的出现 ,有利于合金耐热性的提高。     

Microstructure and mechanical properties of laser melting deposited Ti2Ni3Si/NiTi Laves alloys

Two Ti2Ni3Si/NiTi Laves phase alloys with chemical compositions ofNi-39Ti-11Si and Ni-42Ti-8Si （%, mole fraction, the same below）, respectively, were fabricated by the laser melting deposition manufacturing process, aiming at studying the effect of Ti, Si contents on microstructure and mechanical properties of the alloys. The Ni-39Ti-llSi alloy consisting of Ti2Ni3Si primary dendrites and Ti2Ni3Si/NiTi eutectic matrix is a conventional hypereutectic Laves phase alloy while the Ni-42Ti-8Si alloy being made up of NiTi primary dendrites uniformly distributed in Ti2Ni3Si/NiTi eutectic is a new hypoeutectic alloy. Mechanical properties of the alloys were investigated by nano-indentation test. The results show that the decrease of Si and the increase of Ti contents change the microstructures of the alloys from hypereutectic to hypoeutectic, which influences the mechanical properties of the alloys remarkably. Corrosion behaviors of the alloys were also evaluated by potentiodynamic anodic polarization curves.     

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.     

Evolution of second phases and mechanical properties of 7075 Al alloy processed by solution heat treatment

The effects of solution treatment on the evolution of the second phases and mechanical properties of 7075 Al alloy were studied with scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), differential scanning calorimetry (DSC), hardness and tensile tests. The results show that Mg(Zn, Cu, Al)₂ phases gradually dissolve into the matrix, yet the size and morphology of Al₇Cu₂Fe phase exhibit no change with the increase of the solution treatment temperature and time due to its high melting point. When the solution treatment temperature and time continue to increase, the formation of coarse black Mg₂Si particles occurs. Compared to the as-cast alloy, the microhardness, tensile strength, and elongation of the sample under solution heat treatment at 460 °C for 5 h are increased by 55.1%, 40.9% and 109.1%, respectively. This is because the eutectic Mg(Zn, Cu, Al)₂ phases almost completely dissolve and basically no coarse black Mg₂Si particles are formed.     

Three-dimensional study of Ni aluminides in an AlSi12 alloy by means of light optical and synchrotron microtomography

The three-dimensional (3D) microstructure of an AlSi12Ni alloy in as-cast and in solution-treated conditions is characterized by light optical and synchrotron tomography. Eutectic Al–Si alloys containing 1 wt.% Ni in as-cast condition present networks of connected Si lamellae as well as complex 3D shapes of Ni-containing aluminides. The eutectic Si networks disintegrate during solution treatment in the binary Al–Si alloy while they remain connected in the Al–Si–Ni alloy. The contiguity between eutectic Si and Ni-containing aluminides is maintained, when the alloy is solution treated at 540 °C for 24 h. The sphericity of the aluminides is only slightly increased by the solution treatment. The reinforcing role of eutectic Si together with the Ni-containing aluminides is governed by a stable interconnectivity and contiguity of these rigid phases accumulating ～20 vol.%. The 3D data obtained by synchrotron tomography quantify connectivity, shape and volume fraction of eutectic Si and aluminides, whereas their contiguity is verified by light optical sectioning tomography.     

Gradual solution heat treatment of AlSiCuMg cast alloys

The microstructure characteristics of AlSiCuMg cast alloys were studied with different Cu content and the grad-ual solution treatment by DSC, SEM, TEM and mechanical method. The melting point of α(Al) + Si decreases and poly-nary eutectic phases with low melting point form with increase of Cu content. Gradual solution treatment includes two steps: solution treating near the melting point of polynary eutectic phase to take it dissolve first, and then increasing solution tem-perature to take the remainder copper intermetallics dissolved into α(Al). Grain boundaries melting can be avoided by gradual solution treatment, even the maximum solution temperature is above final solidification point, and the age harden-ing response increases correspondingly.     

铸态和固溶态Mg-8Li-xAl-yZn合金的显微组织与力学性能

研究Al/Zn比(质量比)对Mg-8Li合金显微组织和力学性能的影响.结果发现,对于铸态Mg-8Li-xAl-yZn(x+y=5)合金,当Al/Zn比分别为1:4和2:3时,合金中的第二相主要为AlLi和MgLiZn相;而当Al/Zn比分别为3:2和4:1时,合金中的第二相主要为AlLi和MgLi2Al相.MgLiZn...     

Microstructure characteristics in non-modified and Sr modified Al–Si–Cu–Mg 319 type alloys

Abstract

This study was carried out on 319 alloys containing low and high levels of Mg, in the non-modified and Sr modified conditions (150 ppm Sr addition). Single step, two step and triple step heat treatments were applied to identify the optimum solution heat treatment to minimise incipient melting of the copper phases Al₂Cu and Al₅Mg₈Cu₂Si₆ in these alloys in relation to the alloy properties. In Mg free alloys, no incipient melting of Al₂ Cu was observed even in samples heat treated at 520°C. Addition of Sr leads to modification of Si particles but also to an increase in area per cent porosity and pore length, especially when the solution temperature reaches 520°C. Addition of Mg results in a decrease in the Si particle aspect ratio but an increase in particle size. Magnesium was also found to increase the possibility of incipient melting resulting from the formation of the insoluble Al₅Mg₈Cu₂Si₆ phase. To some degree, Sr decreases the effect that Mg has in increasing the area per cent porosity and pore length, while Mg impairs the effects that Sr has on modifying Si particles, even though the lowest Al–Si eutectic temperature is obtained for the 319 alloy containing both Mg and Sr.     

Microstructures,Compressive Properties,and Microhardness of NiAl-Cr(Mo) Eutectic Alloys With Various Ni Contents

The microstructures and mechanical properties of 66(Ni_xAl)-28Cr-6Mo (x?=?1.0, 1.5, 2.0, 2.5, 3.0, and 3.5) alloys were investigated using scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscope, microhardness, and compression tests. The microstructure of NiAl-28Cr-6Mo (Ni_1.0) eutectic alloy consists of NiAl and Cr(Mo) phases. With increasing the Ni content to 2.0, the microstructure changes from eutectic (Ni_1.0) to eutectic?+?primary NiAl dendrite (Ni_1.5 and Ni_2.0), and the morphologies of part of precipitates in primary NiAl dendrite evolve from granular to needle-like. When the Ni content increases further, besides eutectic and primary NiAl dendrite, the gray phase forms and is identified as an ordered FCC (L1₂) (Ni,Cr)₃(Al,Mo) phase. Moreover, the more needle-like precipitates emerge in the primary NiAl dendrite of Ni_2.5, Ni_3.0, and Ni_3.5 alloys, and the precipitate is identified as a bcc Cr(Mo) phase. The deep etching reveals that the three-dimensional morphology of Cr(Mo) precipitate is not needle-like but lath-like. Among the investigated alloys, both Ni_2.0 and Ni_2.5 alloys possess the higher fracture strength and microhardness. The relevant strengthening mechanisms are discussed.     

Intermetallic phases in Al–Si based cast alloys: new perspective

The present work was performed on experimental Al–Si near eutectic cast alloys, with different additives mainly Fe, Mg, Mn, Cr, Sr and P. The alloys were cooled at 0·8°C s^?1, very close to equilibrium conditions. Precipitated phases, primarily Fe, Cu, Mg and Sr based intermetallics, were examined. Although the phases reported in the present work were documented previously, the range of chemical composition of each phase was confirmed using an electron probe microanalyser equipped with wavelength dispersive spectroscopy and electron dispersive X-ray spectroscopy facilities.     

AlCoCrFeNiTi0.5高熵合金的组织控制和腐蚀性能

研究冷坩埚悬浮熔炼AlCoCrFeNiTi0.5多组元高熵合金的微观组织及回火工艺对合金组织、硬度和电化学性能的影响规律。结果发现,冷坩埚悬浮熔炼AlCoCrFeNiTi0.5高熵合金铸锭中晶粒呈树枝晶长大并析出少量ω相。随回火温度的升高,晶粒长大,共晶组织增多,BCC相强度呈先下降后升高趋势。800℃时,合金树枝晶晶粒变得细小,之后随着温度的升高,枝晶间的元素偏析减弱。合金具有较强的抗回火软化能力。在3.5%NaCl溶液中,孔蚀主要集中在树枝晶与共晶组织α相的交接处,回火后合金的耐蚀性均优于铸态合金,700℃回火后合金的耐腐蚀性能比铸态及其它合金更强。