铝合金点焊过程的铜铝合金化研究

观测了 LF2铝合金电阻点焊初期至达到电极寿命时焊点表面及Cr- Zr- Cu电极端面宏观形貌的连续变化过程。采用扫描电子显微镜( SEM) ,对机加工状态及抛光处理的电极在点焊铝合金后进行了电极端面背散射分析 ,对机加工状态的电极在点焊铝合金后又进行了电极端面横向及纵向线扫描分析。采用 X射线衍射仪 ,对沿电极轴向的 3个不同电极端面进行了 X射线衍射物相分析。结果表明 ,点焊初期 ,焊点表面即出现局部熔化及电极端面出现明显凹凸不平 ,电极端面的形貌及其尺寸发生变化 ,焊点表面成形质量恶化 ,电极端面加工状态对电极端面铜铝合金化影响不大 ,点焊过程电极端面存在较多铝 ,发生了铜铝合金化反应 ,合金化产物主要是铜铝金属间化合物 ( Cu Al2 )。

电极深冷处理与铝合金点焊的铜铝合金化

进行了铝合金点焊电极的深冷处理实验 ,测试了深冷处理电极性能。分别对深冷处理电极和未深冷处理电极进行了铝合金点焊电极寿命试验 ,观测了铝合金点焊过程电极端面及焊点表面宏观形貌。在达到未深冷处理电极寿命时 ,测试了深冷处理和未深冷处理电极端面的显微硬度 ,采用X射线衍射方法对深冷处理和未深冷处理电极端面进行了分析。研究结果表明 ,深冷处理改善了电极的导电、导热等性能 ,使电极端面产热减少 ,降低了铝合金点焊过程的铜铝合金化倾向 。

铝合金点焊电极端面铜铝合金化热物理模拟

针对铝合金电阻点焊过程中出现的电极烧损及使用寿命短的问题,采用物理热模拟的方法,从点焊电极端面铜铝合金化的组织、成分和性能等方面进行了铝合金点焊电极端面铜铝合金化反应的行为和条件研究。研究结果表明:电极端面与工件接触界面发生铜铝合金化反应是铝合金点焊电极烧损的主要原因;铝试样端面生成了C u Al4和C u Al2,铜试样端面主要是C u Al2和少量的C u9Al4,且铜铝扩散层的硬度高于铜基体和铝基体。

铝合金点焊电极端面铜铝合金化机理研究

针对铝合金电阻点焊过程中出现的电极烧损及使用寿命短的问题,采用物理模拟的方法,从点焊电极端面铜铝合金化的宏观及微观形貌、成分等方面,进行了铝合金点焊电极端面铜铝合金化反应的行为、铜铝金属间化的形成过程以及铜铝合金化机理等研究。结果表明:电极端面与工件接触界面发生铜铝合金化反应是铝合金点焊电极烧损的主要原因;同时发现,温度和时间是影响铜铝合金化反应的两个重要因素,且铝合金高温点焊时,电极端面反应生成了共晶合金(Al+Cu Al2),而Cu Al2相和铜基体扩散,将形成硬而脆的金属间化合物Cu9Al4和Cu Al4。

铝合金点焊过程中铜铝合金化的有限元分析

为了研究铜铝合金化反应的机理,本文建立了一种基于铜和铝扩散反应进行的有限元模型。由于热传导方程和扩散方程在表达形式上的相似性,所以用模拟热传导的方式来模拟铝在铜电极中的单向扩散过程,以温度分布表示扩散浓度的分布情况。研究表明:若只考虑铝在铜中的单向扩散,将试验中的数据按比例进行换算,这样计算出来的试验结果与模拟结果比较相近。

铝合金表面氧化膜对点焊电极磨损的影响

铝合金电阻点焊工艺中存在的一个主要技术难题就是电极磨损,探索铝合金点焊电极的磨损机理至关重要。研究了铝合金表面氧化膜对点焊电极磨损的影响,认为电极磨损,除了因为电极与铝合金工件接触面间的铜铝合金化以外,还因为电极与铝合金工件接触面间的不均匀点接触造成通电瞬间的局部爆炸而使铜电极表面产生局部塑性变形,从而引起铜电极表面局部区域的加工硬化,这种局部区域的加工硬化现象与铜铝合金化交互作用,使电极表面的脆化速度加快,电极磨损程度加重。

Strengthening mechanism of T8-aged Al-Cu-Li alloy with increased pre-deformation

The microstructure evolution and mechanical properties of a T8-aged Al-Cu-Li alloy with increased pre-deformation(0-15%) were investigated,revealing the microstructure-strength relationship and the intrinsic strengthening mechanism.The results show that increasing the pre-deformation levels remarkably improves the strength of the alloy but deteriorates its ductility.Dislocations introduced by pre-deformation effectively suppress the formation of Guinier-Preston(GP) zones and provide more nucleation sites for T1 precipitates.This leads to more intensive and finer T1 precipitates in the samples with higher pre-deformation levels.Simultaneously,the enhanced precipitation of T1 precipitates and inhibited formation of GP zones cause the decreases in number and sizes of θ′ precipitates.The quantitative descriptions of the strength contributions from different strengthening mechanisms reveal that strengthening contributions from T1 and θ′ precipitates decrease with increasing pre-deformation.The reduced diameters of T1 precipitates are primarily responsible for their weakened strengthening effects.Therefore,the improved strength of the T8-aged Al-Cu-Li alloy is mainly attributed to the stronger strain hardening from the increased pre-deformation levels.

High temperature mechanical behavior of alumina dispersion strengthened copper alloy with high content of alumina

The microstructure and its effects on the high temperature mechanical behavior of Cu-2.7%Al_2O_3 （volume fraction） dispersion strengthened copper （ADSC） alloy were investigated. The results indicate that fine alumina particles are uniformly distributed in the copper matrix, while a few coarse ones are distributed on the grain boundaries. Tensile tests results show that Hall-Petch mechanism is the main contribution to the yield strength of ADSC alloy at room temperature. Its high temperature strength is attributed to the strong pinning effects of alumina particles on the grain and sub-grain boundaries with dislocations. The ultimate tensile strength can reach 237 MPa and the corresponding yield strength reaches 226 MPa at 700℃. Tensile fracture morphology indicates that the ADSC alloy shows brittleness at elevated temperatures. Creep tests results demonstrate that the steady state creep rates at 400 ℃ are lower than those at 700 ℃. The stress exponents at 400 ℃ and 700℃ are 7 and 5, respectively, and the creep strain rates of the ADSC alloy are controlled by dislocation core diffusion and lattice diffusion.

Enhanced thermal stability and mechanical properties of high-temperature resistant Al-Cu alloy with Zr and Mn micro-alloying

The high temperature(HT)thermal stability and mechanical properties of Al-5%Cu(AC)and Al-5%Cu-0.2%Mn-0.2 Zr%(ACMZ)alloys from 573 to 673 K were systematically studied.The results displayed that micro-alloying additions of Zr and Mn elements have presented a significant role in stabilizing the main strengthening metastableθ′precipitates at a temperature as high as 573 K.Simultaneously,the HT tensile test demonstrated that ACMZ alloy retained their strength of(88.6±8.8)MPa,which was much higher than that of AC alloy((32.5±0.8)MPa)after the thermal exposure at 573 K for 200 h.Finally,the underlying mechanisms of strength and ductility enhancement mechanism of the ACMZ alloy at HT were discussed in detail.

Microstructure evolution and mechanical properties of Al-6.5Cu-0.6Mn-0.5Fe alloys with different Si additions

The effect of Si content on the microstructures and mechanical properties of the heat-treated Al-6.5 Cu-0.6 Mn-0.5 Fe alloy was investigated using image analysis,scanning electron microscopy(SEM),transmission electron microscopy(TEM),and tensile testing.The results show that the mechanical properties of Al-6.5 Cu-0.6 Mn-0.5 Fe alloys decrease slightly when the Si content is below 1.0%.This can be attributed to the comprehensive effect of microstructure evolution,including the increase of nano-sized α-Fe,the coarsened grain size,and an increase in Al2 Cu content at the grain boundary.When the Si content is 1.5%,the mechanical properties of the Al-6.5 Cu-0.6 Mn-0.5 Fe alloys decrease significantly,and this can be attributed to the agglomerated second intermetallics,which is resulted from the formation of excess Si particles.

Friction stir welding of aluminum to copper—An overview

Components made by joining different materials are required in various engineering applications.Fabrication of suchcomponents is a challenging task due to the vast difference in mechanical,thermal and electrical properties of the materials beingused.Friction stir welding(FSW)is capable of joining dissimilar materials such as aluminum(Al)and copper(Cu)and thereforeresearchers have used this novel process for dissimilar joining.Consequently,several works pertaining to dissimilar joining,specifically Al?Cu,are available in the literature but they are scattered in different sources,which makes the task of gatheringinformation about dissimilar FSW of Al?Cu cumbersome.This work has been written with an aim to provide all pertinentinformation related to dissimilar FSW of Al?Cu at one place to ease the problems of researchers.It comprehensively covers andsummarizes the topics such as the effect of tool design and geometry,FSW process parameters,FSW strategies on mechanicalproperties,microstructure and formation of defects during dissimilar FSW of Al?Cu.In addition,it also presents and discussesseveral variants of dissimilar FSW of Al?Cu.Finally,this work not only puts forth major findings of the previous researchers but alsosuggests future recommendations for dissimilar FSW of Al?Cu.

Evolution of surface roughness of a cast Al-Si-Cu piston alloy during thermal exposure

In the present work,samples of Al-Si-Cu piston alloy after T6 heat treatment were exposed for 2 h at temperatures ranging from 400 to 550°C.The evolution of surface roughness and microstructure of the alloy during thermal exposure was studied by combination methods of roughness profiles,optical and scanning electron microscopy as well as XRD analysis.It is found that the roughness and mass of the alloy increase with the raise of the thermal exposure temperature,and the increasing rates of them are slow as the exposure temperature is below 500°C,but accelerates abruptly when the temperature is higher than 500°C.The variation of surface roughness of the alloy is closely related to phase transformation and oxidation during the thermal exposure.

Vacuum Brazing of TiAl Based Alloy with 40Cr Steel

The vacuum brazing of TiAl based alloy with 40Cr steel was investigated using Ag-Cu-Ti filler metal. The experimental results show that the Ag, Cu, Ti atoms in the filler metal and the base metal inter-diffuse toward each other during brazing and react at the interface to form an inter-metallic AlCu 2Ti compound which joins two parts to produce a brazing joint with higher strength.

High Density Plasma Nitriding of Al-Cu Alloys for Automotive Parts

Duralumin alloys have been utilized as structural components and parts for aircrafts, train-cars and so forth. Their high specific strength was attractive to those applications; however, their little corrosion resistance and low wear endurance became a fatal demerit in practical applications. In order to overcome these issues of high strength aluminum alloys, high density plasma nitriding is proposed as an effective surface treatment for duralumin. This process has a capability to control the RF- and DC-plasmas independently for nitriding. This enables us to temporally control and describe the plasma state by in-situ plasma diagnosis. This plasma diagnosis was instrumented to search for optimum processing condition to plasma nitriding the duralumin alloys of type A2011. Both type A2011 aluminum alloy plates and pipes were employed to describe the inner nitriding behavior for hardening the duralumin alloys by the present plasma nitriding.