Development of novel CsF–RbF–AlF3 flux for brazing aluminum to stainless steel with Zn–Al filler metal

Brazing 6061 Al alloy to 304 stainless steel by flame brazing has been carried out with an improved CsF–RbF–AlF₃ flux which matched Zn–xAl filler metals. The results showed that, the spreading area on stainless steel of Zn–xAl filler metals has been improved with the addition of RbF to CsF–AlF₃ flux. It is found that a Zn-rich phase appeared between the brazing seam and the intermetallic compound (IMC) layer in the joints brazed with Zn–2Al and Zn–5Al filler metals, and the thickness of the IMC layer was approximately 1.76–6.45 μm which increased with the increase of Al added to the filler metals. Moreover, a Fe₄Al₁₃ phase formed in the IMC layer, while a Fe₂Al₅ phase appeared as the second layer in Zn–25Al brazed joint. Neither the Zn-rich phase nor Fe₂Al₅ phase was found in the joint brazed with Zn–15Al filler metal, so that the joint was exhibited the maximum shear strength which was up to 131 MPa. All the lap joints were fractured at the interfacial layer of the brazing seam and stainless steel.     

Brazability of dissimilar metals tungsten inert gas butt welding–brazing between aluminum alloy and stainless steel with Al–Cu filler metal

Dissimilar metals tungsten inert gas butt welding–brazing between 5A06 aluminum alloy and SUS321 stainless steel was carried out using Al–Cu6 filler metal and non-corrosive flux. A thin intermetallic compound layer has formed in welded seam/steel interface and the average thickness of the whole layer is 3–5 μm, which is less than the limited value of 10 μm. The intermetallic compound layer consists of Fe₄Al₁₃ phase and at the bottom Sn deposits in the molten flux layer and diffuses into steel matrix to form the grain boundary filter layer, which is the weak zone of the butt joint. The average microhardness of the layer is 644.7 HV, compared with 104.5 HV in welded seam and 200 HV in steel matrix. The tensile strength of butt joint reaches 172.5 MPa and the crack initiates from the IMC layer at the bottom of the joint and derives into welded seam at the upper part of the joint. The present joint in this study has higher level than those with coated layer.     

The microstructure and mechanical properties of fluxless gas tungsten arc welding–brazing joints made between titanium and aluminum alloys

Butt joining of a titanium alloy to an aluminum alloy by gas tungsten arc welding–brazing using an Al-Si eutectic filler wire without flux is investigated. The butt joints have dual characteristics, being a welding on the aluminum side and a brazing on the titanium side. The thickness of the reaction layer varies with position in the titanium alloy interfacial area of the joint, ranging from 2 to 5 μm. At the upper part of interfacial area, the reaction layer includes only the rod-like TiAl₃ phase with 10 at.% dissolved Si. At the bottom of interfacial area, the reaction layer consists of the needle-like τ1 phases (Ti₇Al₅Si₁₂) and the block-like TiAl₃ phase. Hardness of the reaction layer near the welded seam/Ti alloy interface was as much as 400–500 HV. The highest tensile joint strength observed was 158 MPa. Tensile joint failure was by cracks initiating from the reaction layer at the bottom of the joint propagating into the welded seam at the upper part of the joint.     

Interfacial characterization of joint between mild steel and aluminum alloy welded by resistance spot welding

The interfacial characteristics of resistance spot welded steel–aluminum alloy joint have been investigated using electron microscopy. The results reveal that reaction product FeAl₃ is generated in the peripheral region of the weld while a reaction layer consisting of Fe₂Al₅ adjacent to steel and FeAl₃ adjacent to aluminum alloy forms in the central region of the weld, and that the morphology and thickness of the reaction layer vary with the position at the welding interface.     

电弧作用下AlSi5钎料在镀锌钢板上铺展及界面行为研究

采用 TIG 电弧钎焊试验方法,主要研究了电流大小、电弧加热时间以及弧长对 AlSi5钎料在镀锌钢板上润湿铺展及界面行为的影响。实验结果表明：随着电流、燃弧时间和某一范围内弧长的增加,钎料在镀锌钢板上的润湿角逐渐减小,铺展面积逐渐增加,并在某一特定范围时润湿铺展性能达到最佳;随着燃弧电流的增加,界面金属间化合物的厚度呈现先增加后减小的趋势,靠近母材一侧有 Fe2 Al5相生成,钎料一侧则生成 FeAl3相;Al 元素扩散到界面处与 Fe 元素发生扩散反应形成 Fe-Al 金属化合物颗粒,在钎缝中弥散分布着 Si 元素,对钎缝有强化作用。     

Investigation of laser welding on butt joints of Al/steel dissimilar materials

Dissimilar metals of AA6013 aluminum alloy and Q235 low-carbon steel of 2.5 mm thickness were butt joined using a 10 kW fiber laser welding system with ER4043 filler metal. The study indicates that it is feasible to join aluminum alloy to steel by butt joints when zinc layer was hot-dip galvanized at the steel’s groove face in advance, and better weld appearance can be obtained at appropriate welding parameters. The joints had dual characteristics of a welding joint on the aluminum side and a brazing joint on the steel side. The smooth Fe₂Al₅ layer adjacent to the steel matrix and the serrated-shape FeAl₃ layer close to the weld metal were formed at the brazing interface. The overall thickness of Fe–Al intermetallic compounds layers produced in this experiment were varied from 1.8 μm to 6.2 μm at various welding parameters with laser power of 2.85–3.05 kW and wire feed speed of 5–7 m/min. The Al/steel butt joints were failed at the brazing interface during the tensile test and reached the maximum tensile strength of 120 MPa.     

Comparative study on microstructure and mechanical properties of laser welded–brazed Mg/mild steel and Mg/stainless steel joints

A laser welding–brazing (LWB) technology using Mg based filler has been developed for joining Mg alloy to mild steel and Mg alloy to stainless steel in a lap configuration. Microstructure and mechanical properties of laser welded–brazed lap joints in both cases were comparatively studied. The results indicated that no distinct reaction layer was observed at the interface of Mg/mild steel and subsequently the interface was confirmed as mechanical bonding, whereas an ultra thin reaction layer with a continuous and uniform morphology was evidenced at the Mg/stainless steel interface, which was indicative of metallurgical bonding. The newly formed interfacial layer was indexed as FeAl phase by transmission electron microscopy (TEM) combined with energy dispersive spectroscopy (EDS). The average tensile–shear strength of Mg/mild steel joint was only 142 N/mm with typical interfacial failure, while that of Mg/stainless steel joint could reach 270 N/mm, representing 82.4% joint efficiency relative to the Mg alloy base metal. The fracture location of Mg/stainless steel joint was at Mg fusion welding side, suggesting the interface was not weak point due to the formation of ultra thin interfacial layer. The role of alloying elements in base metal and bonding mechanism of the interfacial layer were discussed, respectively.     

Intermetallic Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Al<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>-phases in a steel/Al-alloy fusion weld

The microstructure of joints between an Al-alloy and a zinc coated ferritic steel sheet manufactured by the so-called CMT joining method is investigated. The joint consists of a weld between the Al-alloy and Al 99.8 filler and a brazing of the filler to the zinc coated steel. The morphology, the structure and the defects of the intermetallic phases that developed at the interface between the steel and the Al 99.8 filler are characterised using scanning and transmission electron microscopy. The intermetallic phase seam is only about 2.3 μm thick and consists of trapezoidal nearly equiaxial Fe₂Al₅ grains surrounded by finger-like remains of the steel and mostly elliptical FeAl₃ grains extending into the Al 99.8 filler material. Both the Fe₂Al₅ and the FeAl₃ grains contain crystal defects.     

Ultrasound-assisted brazing of Cu/Al dissimilar metals using a Zn–3Al filler metal

Ultrasound-assisted brazing of Cu/Al dissimilar metals was performed using a Zn–3Al filler metal. The effects of brazing temperature on the microstructure and mechanical properties of Cu/Al joints were investigated. Results showed that excellent metallurgic bonding could be obtained in the fluxless brazed Cu/Al joints with the assistance of ultrasonic vibration. In the joint brazed at 400 °C, the filler metal layer showed a non-uniform microstructure and a thick CuZn₅ IMC layer was found on the Cu interface. Increasing the brazing temperature to 440 °C, however, leaded to a refined and dispersed microstructure of the filler metal layer and to a thin Al_4.2Cu_3.2Zn_0.7 serrate structure in the Cu interfacial IMC layer. Further increasing the brazing temperature to 480 °C resulted in the coarsening of the filler metal and the significantly growth of the Al_4.2Cu_3.2Zn_0.7 IMC layer into a dendrite structure. Nanoindentation tests showed that the hardness of the Al_4.2Cu_3.2Zn_0.7 and CuZn₅ phase was 11.4 and 4.65 GPa, respectively. Tensile strength tests showed that all the Cu/Al joints were failed in the Cu interfacial regions. The joint brazed at 440 °C exhibited the highest tensile strength of 78.93 MPa.     

Arc joining of aluminium alloy to stainless steel with the aid of milling

The aluminium alloy and stainless steel were successfully joined by arc brazing with the aid of milling without using flux at a low heat input. With the increase of the radial cutting depth, more and more strip steel chips appeared in the welded seam, the shear strength of welded seam increased gradually. When the radial cutting depth was 0.10?mm, a very thin and wavy θ-FeAl₃ IMCs layer can be obtained at the joint interface. At this time, there was the maximum value of shear strength of the joint interface (111?MPa). The fracture of joint interface goes through by a fluctuating path.     

Surface wetting and interfacial behaviour in arc brazing of titanium alloy

Abstract

The spreading behaviour of Cu, CuSi, CuMnNi, and TiCuNi filler metals with Ti6Al4V titanium alloy base metal has been studied under gas tungsten arc welding heating. Test results showed that the wet angle of CuMnNi filler metal was the smallest (15 ° ) and that of Cu was the largest (30 ° ). With spreading, the liquid filler metal solidified and crystallised simultaneously, and formed a spherical crown brazing seam. The wettability and spreadability of the liquid filler metal were related to oxide scale actions with arc heating. These actions included the 'cleaning action of the cathode' and lashing activation action of electrifying ions and electrons. Furthermore, the very high temperature of the activation spot zone partly melted the base metal surface and near surface metal, and a thin liquid film was accordingly formed that created a strong heating activation. It was also discovered that there was a column solid - liquid incongruent compound η (MeTi₂) at the interface of filler metal and base metal (Me + Cu, Cu + Ni, Cu + Mn). This compound grew to form an interface with the centre of the brazing seam and was embedded in it. The particular crystallising and growing mode in the arc heating helped grow the column solid - liquid incongruent compound η (MeTi₂).     

CuTiNiZrV Amorphous Alloy Foils for Vacuum Brazing of TiAl Alloy to 40Cr Steel

Vacuum brazing of TiAl alloy to 40Cr steel sheets was conducted with newly developed CuTiNiZrV amorphous foils. It was found that a diffusion layer,filler metal and reaction layer existed in the brazed seam. The diffusion layer in the joint brazed with Cu43.75Ti37.5Ni6.25Zr6.25V6.25(at.%) foil was flat and thin,containing Ti19Al6 and Ti2Cu intermetallic compounds; however,the diffusion layer brazed with Cu37.5Ti25Ni12.5Zr12.5V12.5 foil was uneven with bulges,consisting of essentially Ti-based solute solution. The foil with 12.5 at.% V showed inferior spreadability compared to that with 6.25 at.% V at brazing temperature. However,fracture happened along the diffusion layer with 6.25 at.% V foil due to the formation of brittle intermetallic phases,but the joints brazed with 12.5 at.% V foil failed through the TiAl substrate. These results show that designing amorphous alloy with less Ti and more V for brazing TiAl alloy to steel is appropriate.     

钛合金与铝合金异种金属钎焊的研究进展

钛合金在经济性和加工性方面不理想,导致其在实际工程应用中受限,而铝合金在某种程度上可以弥补这种缺陷,因此将钛合金和铝合金复合使用的构想应运而生。对钛合金和铝合金异种金属的可焊性进行了分析,以钛合金和铝合金钎焊为研究对象,重点论述了钛合金与铝合金钎焊连接所用的钎料及工艺等的国内外研究现状,并着重分析了Al基和Zn基钎料的润湿性、界面、钎缝组织及其优缺点。由相关文献分析可知,Al基钎料在真空、保护气氛或非真空外加辅助措施条件下对钛合金和铝合金都有良好的润湿性,但接头强度仍有待提高,金属间化合物较厚的问题需要通过优化钎料成分和焊接工艺进一步改善;Zn基钎料对钛合金的润湿性较差,但在适当的焊接工艺下可以获得力学性能较好的Ti/Al接头,剪切强度可达141MPa;使用Sn基和Cu基钎料获得的Ti/Al接头的力学性能低于Al基和Zn基钎料,且Sn基的钎料对两种母材的润湿性都较差,需要对母材表面进行预处理。     

Interlayer design for joining pressureless sintered sialon ceramic and 40Cr steel brazing with Ag57Cu38Ti5 filler metal

An interlayer design and test was made to enhance the joining strength of the pressureless sintered sialon ceramic and 40Cr steel. Joining was preformed by vacuum brazing using Ag₅₇Cu₃₈Ti₅ filler metal. The joint strength was evaluated by four-point bending. A strong interfacial bond of the Ag₅₇Cu₃₈Ti₅ filler metal on the sialon ceramic with formation of Ti₂AlN, Ti₅Si₄ and TiAg was obtained at brazing temperatures over 1123 K, which could be weakened by a brazed metal such as Kovar or Ni-15Cr-15Co alloy. The joint strength of sialon ceramic with 40Cr steel can be improved by using a layer of soft interlayer such as Cu with a suitable thickness, particularly by the composite interlayer such as Cu/Nb alloy, Cu/Ta, Cu/Mo etc. The maximum strength of the ceramic/steel joint, 280 MPa, was obtained by using Cu/Nb alloy as interlayer and brazing at 1153 K for 5 min. Finally, we discuss how to design an interlayer in ceramic/metal joining.     

铝-镀锌钢板异种金属Pulsed DE-MIG熔钎焊方法研究

为精确控制焊接热输入,从而控制铝钢异种金属界面区金属间化合物生长,提出一种新型高效低热输入的脉冲旁路耦合电弧MIG焊(Pulsed DE-MIG)方法,用ER5356铝合金焊丝在镀锌钢板上利用平板堆焊实验对工艺参数进行优化.在焊丝总电流保持不变,不同的Pulsed DE-MIG焊接参数下焊接,结果表明随着旁路电流的增大,焊缝宽度显著变小,且焊缝堆高明显变高.采用OM、SEM、EDS等测试手段观察和分析连接界面区的微观组织,发现在连接界面区形成Fe2Al5、FeAl3金属间化合物层,且母材热输入大时,FeAl3析出得多,随着母材热输入的减小,FeAl3析出逐步减少直至FeAl3无析出.     

Formation of the reaction zone between tin‐copper brazing fillers and aluminum‐silicon‐magnesium alloys: Experiments and thermodynamic analysis

A primary challenge in brazing is the controlled formation of phases resulting from interactions of elements of the liquid filler metal with those of the base material. The morphology of the brazed joint, which is decisive for the mechanical properties of the joint, is influenced by present elements and process parameters such as brazing temperature and time. Furthermore, the wetting of the base material is a crucial factor in joining of aluminum because of the low wettability of the alumina layer by molten brazing filler metals. In order to remove the alumina and prevent reoxidation of the substrate surface, the brazing process can be conducted in vacuum or inert gas atmosphere. Again, selection of process parameters is crucial for the quality of the brazed seam. In this work, we focus on the influence of the process parameters on the wetting behavior and the formation of aluminum‐copper phases theoretically by means of thermodynamic calculations using a CALPHAD database as well as by means of in‐situ observations in the large‐chamber scanning electron microscope (LC‐SEM) and by brazing experiments. Both the critical temperatures with respect to the wetting and the reaction kinetics as well as the crucial stages of the brazing process and the resulting phases were determined.     

焊丝成分对铝-铜异种金属熔钎焊接头钎焊界面组织与接头力学性能的影响

采用脉冲旁路耦合电弧MIG熔钎焊方法对1060纯铝和T2紫铜进行了对接焊,选用ER1100、ER5356、ER4043和ER4047四种焊丝为填充材料,研究了焊丝成分对焊接接头微观组织、金属间化合物层的厚度以及力学性能的影响规律。结果表明:4种焊丝的焊接接头均由铝侧熔合区、焊缝区和铜侧钎焊区组成,其中铜侧钎焊区又可细分为金属间化合物层区和Al-Cu共晶区两部分。焊丝中Si元素的加入可以起到阻碍铝铜原子互扩散、抑制铝铜金属间化合物生长、提高焊缝显微硬度以及抗拉强度等作用;而加入Mg元素,其效果不明显。     

采用BNi-7的Ti（C，N）基金属陶瓷与17-4PH沉淀硬化不锈钢的真空钎焊研究

采用镍基共晶钎料BNi-7对Ti（C,N）基金属陶瓷与17—4PH沉淀硬化不锈钢行了真空钎焊连接。研究了钎焊温度和焊缝厚度对焊接接头力学性能和微观结构的影响。结果表明,BNi-7对金属陶瓷粘结相具有较强的溶解能力,这是熔降元素（磷）能够在金属陶瓷侧大范围分布、钎焊接头获得良好界面结合的主要原因。随钎焊温度升高,磷在金属...     

Interface and Bond Strength of Brazing Cemented Carbide K20 to Alloy Steel AISI 4140 by High-Frequency Induction

High-frequency induction brazing of cemented carbide (WC–Co, K20) and alloy steel (AISI 4140) using Cu–Zn base filler metal was carried out. The relationship between microstructure and performance of the welding joint was investigated. It was found that the filler metal exhibited excellent wettability and metallurgical bond in the welding surface. As the heating rate reduced, welding joint appeared smooth without any visible crack. In the diffusion layer, some intermetallic compounds were observed, which were produced by the reaction of diffusion atoms. The microhardness in the middle of the welding seam was 168 Hv and it increased gradually when approaching to the edge of welding seam. With brazing temperature increased or heating rate decreased, the shear strength of welding joint increased first and then decreased. The machining test clearly revealed that the cutting temperature and the flank wear increased with the cutting speed rose. The welding joint had good shear strength when the temperature was below 500°C and the shear strength decreased seriously when the temperature exceeded 500°C.     

不基于熔态润湿的Al/Al2O3直接钎焊

针对Al熔液在850℃以下不润湿Al₂O₃而难以直接钎焊的困难, 本工作研究了溅射Al对Al₂O₃的“润湿”作用, 提出了一种采用溅射Al基薄膜作为钎料直接钎焊Al₂O₃的方法。结果表明, 这种方法可以在不满足熔态Al润湿条件的680℃实现Al和Al-Cu合金对Al₂O₃的直接真空钎焊, 并且仅需0.1 Pa的真空度。所获得的Al/Al₂O₃的接头剪切强度达到115 MPa, Al-1.6at% Cu合金钎焊接头的剪切强度可提高到163 MPa, 当钎料中的Cu含量提高至14.3at%后, 钎焊接头中焊缝与陶瓷界面产生Cu的偏聚, 接头的剪切强度因界面断裂降低为127 MPa。并对这种不基于金属熔态润湿钎焊方法的原理进行了分析讨论。