Brazeability of a 3003 Aluminum alloy with Al-Si-Cu-based filler metals

Al-Si-Cu-based filler metals have been used successfully for brazing 6061 aluminum alloy as reported in the authors’ previous studies. For application in heat exchangers during manufacturing, the brazeability of 3003 aluminum alloy with these filler metals is herein further evaluated. Experimental results show that even at such a low temperature as 550 °C, the 3003 alloys can be brazed with the Al-Si-Cu fillers and display bonding strengths that are higher than 77 MPa as well. An optimized 3003 joint is attained in the brazements with the innovative Al-7Si-20Cu-2Sn-1Mg filler metal at 575 °C for 30 min, which reveals a bonding strength capping the 3003 Al matrix.     

Corrosion of AD31 (AA6063) Alloy in Chloride-Containing Solutions

Corrosion of AD31 (AA6063) alloy in neutral 0.05 M NaCl solutions is investigated via scanningprobe microscopy, linear-sweep voltammetry, and electrochemical-impedance spectroscopy. Al?Fe?Si?Mg intermetallic particles are determined to prevail in the structure of alloy and act as local cathodes. Intermodulation electrostatic-force-microscopy imaging shows that their Volta potential differs by 570 mV from that of the host aluminum matrix, making the alloy prone to localized corrosion. We show that the corrosion of alloy in the studied electrolyte mainly develops locally and results in pitting, with charge transfer being the limiting stage of the process. A mechanism of corrosion of the AD31 (AA6063) alloy in neutral chloride-containing solutions is proposed.     

Effect of brazing parameters on fillet size and microstructure of cladded fin-microchannel tube joints

This work concerns the optimization of furnace brazing conditions for joining micro-multiport aluminum tubes and fins made with AA4343/AA3003/AA4343 brazing sheet in mini-assemblies mimicking the core of an automotive heat exchanger. Taguchi method was used for design of experiment, considering five process parameters with two levels of values. The aim was to maximize the fillet size of the brazed joints, which has an important influence on the thermal integrity and mechanical properties. Fillet length measurements of brazed joints were performed with a metallographic microscope. The statistical analysis allowed to obtain the optimum values of process parameters (peak temperature, residence time, heating rate, microchannel tube type and flux). At a 95% confidence level, the variability of fillet length is most significantly affected by the peak brazing temperature (77%), residence time (15%) and heating rate (7%). The predicted maximum fillet length was (152±11) µm, which was corroborated by confirmation trials. The microstructural analysis of tube−fin joints showed that variations in peak temperature and residence time affect only the size of the eutectic zone of fillet formed, but not the nature or composition of the constituent phases.     

Influence of heat treatment and surface conditioning on filiform corrosion of aluminium alloys AA3005 and AA5754

The effect of high-temperature heat treatment combined with different cleaning and pre-treatment practices on filiform corrosion resistance has been investigated for aluminium alloys AA3005 and AA5754. High-temperature heat treatment severely reduces the filiform corrosion resistance of alloy AA3005, while the corrosion properties of alloy 5754 are only moderately affected. The drastic loss of filiform corrosion resistance of alloy AA3005 after high-temperature heat treatment is attributed to preferential microstructural changes in a heavily deformed, micrograined surface layer caused by large surface shear strain during rolling. The enhanced deformation of the near-surface region promotes precipitation of a fine dispersion of intermetallic particles during subsequent heat treatment. The higher density of intermetallic particles combined with lower supersaturated solid solution levels of manganese in the surface layer as compared to the bulk structure makes the heat-treated AA3005 material susceptible to superficial corrosion attacks and results in poor filiform corrosion resistance. Application of a commercial acid cleaning/chromating pre-treatment did not restore the filiform corrosion resistance of heat-treated alloy AA3005. Alloy AA5754, containing lower levels of manganese and iron than AA3005, did not undergo similar preferential microstructural changes during heat treatment. A moderate increase in the amount of filiform corrosion of heat-treated AA5754 samples is attributed to poor protective properties of the thick, magnesium enriched, thermally formed surface oxide on this alloy. Any cleaning/pre-treatment practice that removes the thermally formed oxide on this alloy results in a very high filiform corrosion resistance.     

均匀化处理对AA3003铝合金铸轧板再结晶组织的影响

采用光学显微镜、硬度仪、扫描电镜、双臂电桥等手段,研究了均匀化处理对AA3003铝合金铸轧板组织、析出相和再结晶温度的影响。结果表明,高温均匀化退火对AA3003铝合金的再结晶具有显著地促进作用。铸轧板经580℃均匀化退火5h,冷轧后合金的再结晶温度明显降低,并且再结晶后得到尺寸梯度很小的等轴晶组织。     

Effect of surface treatments based on self‐assembling molecules and cerium coatings on the AA3003 alloy corrosion resistance

This work presents the effects of a cerium conversion coating, self‐assembling molecules (SAM) treatment, and a combination of these two treatments on the corrosion resistance of the AA3003 alloy. The results were compared to that of a conversion coating treatment with hexavalent chromium (Cr VI). The corrosion resistance of the surface‐treated AA3003 alloy samples was investigated by electrochemical impedance spectroscopy and anodic polarization curves in 0.5 mol/L sodium sulfate solution with pH adjusted to 4.0. The results showed that the SAM treatment offered better corrosion protection for the AA3003 alloy than that provided by cerium conversion coating. The combination of cerium conversion and SAM treatments improved the corrosion resistance of the AA3003 alloy due to SAM adsorption on the alloy substrate exposed at the defects in the cerium conversion layer.     

冷加工对含Mn铝合金管腐蚀行为的影响

采用SEM,TEM,动电位极化和浸泡实验研究了机械冷加工变形对汽车散热器高Mn(0.22%,质量分数,下同)和低Mn(0.08%)铝合金管在0.6 mol/L NaCl(pH=6)和SWAAT(ASTM G85,pH=3)溶液中的腐蚀行为的影响.电化学极化测试表明,无形变时高Mn铝合金直管的点蚀电位最高;但冷加工能降低高Mn铝合金弯曲表面的点蚀电位,而对低Mn铝合金的点蚀电位没有明显影响.TEM观察发现,冷加工后高Mn铝合金中有大量纳米尺度的富Mn析出相,在低Mn铝合金中却没有观察到这种析出相,阴极极化测试表明,富Mn相能显著促进阴极反应,富Mn相相对Al基体为阴极相,因而是点蚀萌生的部位.添加Mn尽管有利于提高铝合金的耐蚀性,但机械冷加工会弱化这一效应.     

封条式铝合金热交换器氮气保护钎焊失效分析

封条式铝合金热交换器用途广泛、可靠性高,采用氮气保护钎焊具有生产效率高、温度均匀性好、成本低等特点。本研究介绍了封条式铝合金热交换器的结构特点、材料和用途,并介绍了适用于氮气保护钎焊批量生产的钎焊设备、流程、方法和参数。钎焊是产品生产的关键工序,钎焊失效往往导致产品报废,合格率的下降,进而导致成本的上升。本研究把在生产实践中遇到的主要失效模式根据失效件的特点分为顶板变形、零件移位或变形、温度超高或过低、钎缝泄漏等4大类,分别对这各类失效模式产生原因进行了分析,并针对失效模式的根本原因,从钎焊夹具设计、过程管理、钎焊工艺、零件清洁等方面提出了预防与改进措施,在生产实践中取得了良好效果。     

车辆热交换器铝合金管的高频焊接

管材所用铝合金带料为三层复合材料,外层为Al-Si钎料层,中间为Al-Mn芯材,内层为Al-Zn防腐层。带材经成型机组成型后经高频焊接而成。研究表明:采用高频焊接铝合金管焊缝成形美观、无气孔等缺陷,焊速高,焊缝微观组织均匀,是一种理想的焊接工艺。     

Solidification studies of automotive heat exchanger materials

Modifications of the aluminum alloy AA 3003 have been studied to improve and tailorits properties for applications in automotive heat exchangers. Laboratory techniques have been applied to simulate industrial direct-chill casting, and some basic solidification studies have been conducted. The results are coupled to structures observed in industrial-size ingots and discussed in terms of structure-property relations.     

车辆热交换器铝合金管的高频焊接

管材所用铝合金带料为三层复合材料，外层为Al-Si钎料层，中间为Al-Mn芯材，内层为Al-Zn防腐层。带材经成型机组成型后经高频焊接而成。研究表明：采用高频焊接铝合金管焊缝成形美观、无气孔等缺陷，焊速高，焊缝微观组织均匀，是一种理想的焊接工艺。     

Diffusional solidification phenomena in clad aluminum automotive braze sheet

Differential scanning calorimetry (DSC) was used to investigate clad/core interactions and the evolving microstructure during simulated brazing of aluminum brazing sheet alloy No. 12, which consists of an AA3003 core with AA4343 cladding layers on either side. During the brazing operation the clad layers can alloy with the core as a result of Si diffusion before and after clad melting (i.e. in the solid-state and the solid/liquid state). This interaction affects the amount of liquid formed and its duration, which will impact on joint formation and mechanical performance. Metallographic data and DSC liquid fraction measurements show that solid-state interdiffusion prior to melting is responsible for some initial liquid suppression, but the amount of liquid present during the brazing cycle decreases rapidly as a result of isothermal, or diffusional, solidification. The liquid phase can be completely removed via diffusional solidification at the brazing temperature prior to cooling, leaving behind a significantly coarsened clad structure. Using this novel and practical DSC technique, experimental insight regarding Si diffusion into the core can be obtained as well as the evolving clad/core solidification structure.     

Zr元素对Al-Mn-Si-Zn系铝合金组织与性能的影响

研究Zr添加对Al-Mn-Si-Zn合金显微组织、力学性能及电化学性能的影响。透射电镜观察表明,Zr合金化可使退火态合金中的析出相更加细小、弥散,但是对模拟钎焊态合金的影响较弱。拉伸实验结果表明,添加Zr能够显著提高退火态合金的力学性能,但是对模拟钎焊态合金影响不大。电化学实验结果则表明,Zr元素的添加可降低退火态合金的抗腐蚀性能,但是对模拟钎焊态合金的影响不大。     

Using EIS to study the electrochemical response of alloy AA5083 in solutions of NaCl

The corrosion behavior of alloy AA5083 in aerated solutions of NaCl has been studied. Special attention has been paid to the analysis of the electrochemical response of this alloy using Electrochemical Impedance Spectroscopy (EIS). Analysis of the obtained data has enabled an evaluation of the contributions made by each of the corrosion processes active in the system: localized alkaline corrosion in the areas surrounding the intermetallic precipitates and growth of the layer of oxide on the matrix. It has been determined that the process of localized corrosion has the greatest verifiable intensity, but this process reduces with length of exposure time.     

Microstructure influence on corrosion behavior of a Fe–Cr–V–N tool alloy studied by SEM/EDS,scanning Kelvin force microscopy and electrochemical measurement

Microstructure influence on corrosion behavior of an N-based tool alloy (Fe–Cr–V–N) has been studied. Electron microscopy analysis showed two types of hard phases in the alloy. One-pass mode scanning Kelvin force microscopy (KFM) was used to investigate relative nobility of the hard phases. Volta potential mapping indicates higher nobility for the hard phases than the alloy matrix, and, the V- and N-rich particles exhibit the highest Volta potential. Post-polarization analysis by SEM revealed localized dissolution initiated in matrix regions adjacent to hard phase particles, and the boundary region surrounding the Cr- and Mo-rich particles is more prone to localized corrosion.     

Effect of solution heat treatment on galvanic coupling between intermetallics and matrix in AA7075-T6

Susceptibility to localised corrosion is strongly affected by heat treatments performed on Al-Zn-Cu-Mg alloys. In order to study how galvanic coupling between intermetallics and matrix is affected by solution heat treatment, AA7075-T6 and solution heat treated AA7075 have been characterised by means of scanning electron microscopy and scanning Kelvin probe force microscopy. Solution heat treatment strongly increased the Volta potential difference between the intermetallics and the surrounding matrix showing a strong increase in galvanic coupling. This is explained by Zn and Mg enrichment of the matrix caused by dissolution of strengthening particles during solution heat treatment.     

Corrosion behaviour of brazed multilayer material AA4343/AA3003/AA4343: Influence of coolant parameters

This paper is the second part of a work devoted to corrosion in brazed AA4343/AA3003/AA4343 materials on the water side of automotive heater cores. In the first part of the study [S. Tierce, N. Pébère, C. Blanc, C. Casenave, G. Mankowski, H. Robidou, Electrochim. Acta 52 (2006) 1092], corrosion initiation in the surface layer (i.e. the residual cladding) has been investigated. It has been associated to defective sites in the passive film covering the alloy. The defective sites are linked to α-Al(Mn,Fe)Si particles built up during brazing process. Interactions between α-Al(Mn,Fe)Si particles and the matrix are responsible for the observed behaviour. The present study focuses on the propagation of corrosion through the material in neutral water–ethylene glycol mixtures with and without chlorides. Comparison of the electrochemical behaviour of the three layers of the brazed material (i.e. the residual cladding, the “band of dense precipitates (BDP)” and the core material) revealed that the residual cladding was nobler than the BDP and the core material and thus that the corrosion should propagate through the inner layers due to galvanic coupling: the inner layers constitute the anode and the residual cladding the cathode. Increasing the ethylene glycol content in the water–ethylene glycol mixture decreased the rate of consumption of the materials whereas addition of chloride ions increased it. Mass variation measurements of brazed material in different solutions containing the degradation products of ethylene glycol showed that only glycolate ions had a slight detrimental effect. Corrosion tests performed in heater core tubes allowed the propagation mechanisms to be confirmed.     

Analytical characterisation and corrosion behaviour of bis-[triethoxysilylpropyl]tetrasulphide pre-treated AA2024-T3

This work aims at studying the corrosion behaviour of AA2024-T3 pre-treated with bis-[triethoxysilylpropyl]tetrasulphide. Simultaneously, the work investigates the influence of the Cu-rich intermetallic particles on the formation of the silane film. The analytical characterisation of the silane films was performed by Auger electron spectroscopy and X-ray photoelectron spectroscopy. The corrosion performance of the pre-treated substrates was evaluated by electrochemical impedance spectroscopy. Atomic force microscopy associated with Kelvin probe was also used to determine the influence of the silane film on the Volta potential distribution on the alloy surface. The results show that copper present in the intermetallics plays an important role on the film formation.     

动态再结晶特征及其对黄铜腐蚀敏感性的影响

研究了具有不同组织结构的铜合金管材在淡水中的腐蚀行为。合金存在大量粒径小于5µm的晶粒,且大小晶粒差别显著,表现为不完全再结晶的组织结构。大量细小晶粒的存在增加了铜合金在淡水中的腐蚀敏感性,主要表现为表面膜层不稳定、膜层鼓泡脱落、出现微裂纹和沿晶腐蚀。不完全再结晶的组织可以形成腐蚀通道,使合金的腐蚀迅速向纵深发展。这种组织来源于热加工中的动态再结晶过程,因某种原因保留到了冷加工及其热处理过程之后。     

ZL102铝合金在3% NaCl溶液中的微区电化学特性

采用扫描电化学显微镜技术(SECM)深入研究了ZL102铝合金在3%NaCl(质量分数)溶液中的腐蚀行为,用光学显微镜和扫描电镜观察其腐蚀形貌,用能谱仪对夹杂物和腐蚀产物进行分析。结果表明:在3%NaCl溶液中,金属间化合物与ZL102铝合金基体形成微电池,金属间化合物的电位高于基体的,使基体优先腐蚀溶解;腐蚀过程中铝合金表面活性不稳定,是因为尺寸较小的金属间化合物因周围基体溶解容易脱落,并在其他区域沉淀,只有尺寸较大的金属间化合物周围基体产生持续腐蚀溶解,最终形成点蚀。