Laser pressure welding of aluminium and galvannealed steel

Dissimilar metal joints of galvannealed steel and commercially available pure aluminium (A1050) sheets were produced by changing the laser power and the roller pressure by the laser pressure welding method. In this method, the YAG laser beam was irradiated into a flare groove made by these dissimilar metal sheets. In addition, the laser beam was scanned at various frequencies and patterns through the fθ lens using two-dimensional scanning mirrors. Then the sheets were pressed by the pressure rolls to be joined. The compound layers in the weld interface were observed by optical microscope, and the layer thicknesses were measured. The thicknesses were in the range of 7–20 μm. The mechanical properties of welded joints were evaluated by the tensile shear test and the peel test. In the tensile shear test, the strengths of the joints produced under the most welding conditions were so high that the fracture occurred through the base aluminium sheet. In the peel test of the specimens subjected to the laser beam of 1200–1400 W power under the roller pressure of 2.94 kN, the specimen fracture took place in the base aluminium sheet. Even if the compound layer was thick, high joint strength was obtained. In order to know the reason for such high strength of joints with thick compound layers and the joining mechanism, the compound layer was observed by the HR-TEM. The TEM observation results revealed that the main phase in the compound layer was the solid solution of Al + Zn. Moreover, the intermetallic compound was identified as FeAl, Fe₂Al₅, Fe₄Al₁₃, and Fe₂Al₅Zn_0.4 phase by electron diffraction. The Fe₃Zn₁₀ (Γ phase) of Fe–Zn intermetallic compound was confirmed on a Fe base material. It is assumed that the joining areas were heated in a range of 782°C more than 665°C, a melting point of Al, by laser irradiation because the δ_lk phase aspect was not confirmed. Because the surfaces of A1050 and Zn plated layer were melted thinly, the layer was over 10 μm thicker. The reason for the production of high strength joints with the relatively thick intermetallic compound layer was attributed to the formation of (Al + Zn) phase with finely dispersed intermetallic compounds.     

Mechanical properties of laser-pressure-welded joint between dissimilar galvannealed steel and pure aluminium

Dissimilar metal joints of Zn-coated Galvannealed steel (GA steel) and commercially available pure aluminium (A1050) sheets were produced by changing the laser power and the roller pressure by the laser pressure welding method. By this method, the YAG laser beam was irradiated into a flare groove made by these dissimilar metal sheets. In addition, the laser beam was scanned at various frequencies and patterns through the fθ lens using two-dimensional scanning mirrors. Then the sheets were pressed by the pressure rolls to be joined.

The compound layers in the weld interface were observed by an optical microscope and the layer thicknesses were measured. The thicknesses ranged from 7 to 20 μm. The mechanical properties of the welded joints were evaluated by the tensile-shear test and peel test. In the tensile-shear test, the strengths of the joints produced under the most welding conditions were so high that the fracture occurred through the base aluminium sheet. In the peel test of the specimens subjected to a laser beam of 1200–1400 W power under roller pressure of 2.94 kN, the specimen fracture took place in the base aluminium sheet. Even if the compound layer was thick, high joint strength was obtained. On the other hand, the specimen fractured in the weld interface at a laser power of 1500 W. The results of X-ray diffraction on the peel test specimen surface identified that the intermetallic compound on the GA steel side was Fe₂Al₅Zn_0.4. Moreover, the aluminium parts adhering to the GA steel side were confirmed. These results suggest that the fracture in the peel test occurred between the compound layer and A1050 and partly in the base aluminium. A micro-Vickers hardness test was performed to examine the hardness distribution in the compound layer. The hardness values near A1050 and GA steel were about 100 and 470 Hv, respectively, which suggests that the compound layer should not necessarily consist of brittle intermetallic compounds. It is therefore concluded that laser pressure welding could produce high strength joints of GA steel and A1050 dissimilar materials.     

Effect of gas flow rate on shapes of weld bead sections. Study on high‐speed surface treatment by arc with laser (2nd report)

Recently, lightening, speed-up and decreasing vibration of the transport vehicles have been discussed for improving of environmental problems. As one solution, the material hybrid concept using aluminum alloys and high strength steels has been proposed. Therefore, new welding processes by which these dissimilar materials can be joined in high reliability and productivity are demanded. Laser roll welding was developed for joining of dissimilar metals by M. Kutsuna, M. Rathod and A. Tsuboi in 2002. Up to now, a CO₂ laser has been used as a heat source. In the present work, laser roll welding of low carbon steel and aluminum alloy using a 2 kW fibre laser was investigated to improve the joint properties due to the effective heating characteristics. Effects of the process parameters were studied. Otherwise, the influences of process parameters on the weldability, the formation of intermetallic compound layer and the mechanical properties have been investigated. As a result, various types of intermetallic compound layer were confirmed at the laser roll welded joint interfaces. When intermetallic compound layer thickness was less than 10 μm, the specimen was a failure in the base metal of low carbon steel in the tensile shear test.     

铝/钢固态焊接合界面金属间化合物生长机制

在保持固态条件下,分别变化加热温度、时间对铝/Q235钢爆炸焊接头进行加热处理.分析了接合界面区反应层形貌等微观特征,探讨了加热温度、加热时间对反应层厚度的影响,研究了接合界面金属间化合物的生长行为.界面反应物是由靠近铝合金侧的反应物为Fe₄Al₁₃和靠近钢侧反应物为Fe₂Al₅构成.金属间化合物层随着加热时间的延长而变厚.结果表明,金属间化合物的生长满足抛物线法则,其生长激活能为33.26 kJ/mol.     

Effects of resistance spot welding parameters on microstructures and mechanical properties of dissimilar material joints of galvanised high strength steel and aluminium alloy

Abstract

Intermediate frequency resistance spot welding has been adopted to join dissimilar materials of H220YD galvanised high strength steel and 6008 aluminium alloy. The effects of welding current and welding time on microstructures and mechanical properties of the welded joints were investigated. A thin intermetallic compound layer composed of Fe₂Al₅ phase and Fe₄Al₁₃ phase formed at the steel/aluminium interface. The interfacial intermetallic compound layer has higher nanohardness compared with the aluminium alloy nugget and galvanised steel. With increasing welding current (4–11?kA) and welding time (50–300?ms), the nugget diameter increased, the interfacial layer structure became coarser and the tensile shear load of the welded joints had an increased tendency. The maximum tensile shear load reached 3309?N at 9?kA for 250?ms. Crack initiated at the interfacial intermetallic compound layer of the tensile shear specimens, then propagated through the interfacial layer principally, and meantime through the aluminium alloy fusion zone near the interface partially.     

Intermetallic compounds in friction stirred lap joints between AA5754/galvanised ultra-high strength steel

This paper presents results of joining of AA5754 and DP800 based on the friction stir welding process. Joints were produced by the tool made of H13 tool steel which was allowed to penetrate through the aluminium sheet until reaching the surface of steel sheet without penetrating into it. This approach is an economic and robust way to operate the dissimilar welding process without excessive tool cost. Bonding was achieved by interfacial diffusion reactions between aluminium and iron with a formation of intermetallic compounds. The formation of brittle intermetallic compounds at the interface between the materials was studied. Three intermetallic phases were found at the interface including Al₁₃Fe₄, Al₅Fe₂ and Fe₃Zn₁₀. A range of process parameters was identified with a thickness of the intermetallic layers around 2?µm. Shear fracture failure mode was observed under overlap loading. The mechanisms of formation of the joints and factors controlling the strength were discussed.     

铝/钢异种金属电弧辅助激光对接熔钎焊方法

采用小功率TIG焊电弧辅助激光热源进行5A06铝合金和热镀锌钢ST04Z对接熔钎焊工艺试验,获得表面成形连续、美观的焊缝.采用SEM,EDS,XRD,拉伸试验机、显微硬度计对熔钎焊接头的微观组织和力学性能进行了研究.结果表明,与单纯激光相比,电弧辅助激光热源改变了焊接过程的温度场分布,从而促进液态铝向钢侧的铺展,所得对接接头最大抗拉强度可达到163 MPa,约为5A06铝合金母材抗拉强度的74%,是激光焊接头强度的1.3倍.接头过渡层形成的金属间化合物以脆硬的Fe₂Al₅,Fe₄Al₁₃为主.拉伸断裂起始于脆性的金属间化合物层,终止于韧窝断裂.     

The Zn-Rich Corner of the Zn-Fe-Al-Sb Quaternary System at 450 °C

The 450 °C isothermal section of the Zn-Fe-Al-Sb quaternary system with Zn fixed at 93 at.% has been studied experimentally using x-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy. The (L + AlSb) field is in equilibrium with other phase fields in the section, except those near the 93Zn7Fe corner. The solubility of Sb in ζ, δ, T, Fe₂Al₅, and FeAl₃ phases is very limited. The Zn-Fe-Al ternary phase T (Al₆Fe₈Zn₈₆) was found to be in equilibrium with L, δ, Fe₂Al₅, and AlSb phase. The maximum solubilities of Zn in AlSb, Fe₂Al₅, and FeAl₃ are 5.3, 12.3, and 6.2 at.% respectively. Zn can be dissolved in all compounds existing in the equilibrium alloys. Five four-phase regions and four three-phase regions have been confirmed experimentally.     

镁与镀锌钢板脉冲旁路耦合电弧熔钎焊

采用脉冲旁路耦合电弧熔钎焊,使用AZ92A镁合金焊丝在镀锌钢板上进行平板堆焊试验,通过调整焊接工艺参数,能在最佳的焊接参数下得到熔宽均匀,成形良好的焊缝.通过SEM,EDS,EPMA等测试手段对焊接接头界面中心区的微观组织进行观察与分析,及对焊缝的剥落面进行XRD测试发现有Mg₁₇Al₁₂,Mg_0.97Zn_0.03和Fe₄Zn₉金属间化合物形成.结果表明,在适当参数下,利用脉冲旁路耦合电弧熔钎焊可获得镁与镀锌钢板的焊缝,且镁与镀锌钢板异种金属电弧熔钎焊时镁和铁都与锌反应形成了金属间化合物.     

Annealing Effect on the Intermetallic Compound Formation of Cold Sprayed Fe/Al Composite Coating

A Fe/Al composite coating was prepared by cold spraying using an iron-aluminium powder mixture with a Fe/Al atomic ratio of 1:1. The effect of annealing temperature on the intermetallic compound formation in the cold-sprayed Fe/Al coating was investigated. The as-sprayed and annealed coatings were characterized by x-ray diffraction (XRD), and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy. Results showed that intensive particle deformation on impact promoted the Fe₂Al₅ intermetallic compound formation at a low annealing temperature of 450?°C and this intermetallic layer firstly appeared along some intimate contact regions at the aluminium-iron boundaries. The amount of the Fe₂Al₅ intermetallic compound increased and no other intermetallic compound phases appeared when the annealing temperature was raised from 450 to 600?°C. Some cracks developed in the Fe₂Al₅ intermetallic layer when the coating was annealed at 600?°C and the possible causes leading to evolution of cracks are discussed.     

铝-钢异种金属脉冲旁路耦合电弧MIG熔钎焊界面反应的热力学分析

采用脉冲旁路耦合电弧MIG熔钎焊方法用ER5356铝合金焊丝在镀锌钢板上进行平板堆焊试验.通过调整焊接参数获得最佳焊接成形,结果表明脉冲旁路耦合电弧MIG熔钎焊方法可以实现铝和铁异种金属材料的连接.采用SEM,EDS等测试手段观察和分析连接界面区的微观组织,在连接界面区形成Fe₂Al₅,FeAl₃金属间化合物层.通过Thermo-Calc软件对Fe₂Al₅,FeAl₃金属间化合物的吉布斯自由能进行计算,得出在高温Fe₂Al₅的吉布斯自由能比FeAl₃的吉布斯自由能小,在低温FeAl₃的吉布斯自由能比Fe₂Al₅的吉布斯自由能小,说明在焊接过程中Fe₂Al₅金属间化合物先生成,再在冷却过程中FeAl₃金属间化合物生成或析出.     

Effect of lattice matching degree and intermetallic compound on the properties of Mg/Al dissimilar material welded joints

The welding of Mg/Al dissimilar materials with different filler metal was investigated, and the quantities and kinds of intermetallic compounds were discussed. In addition, the matching degrees between base metal and intermetallic compounds were defined and calculated, and the effect of different quantities of each intermetallic compound on the property of welded seam was investigated. The results indicated that the welded seam was composed of Al₃Mg₂ and Al₁₂Mg₁₇ by Mg/Al directly gas tungsten arc butt welding, and only one intermetallic compound of MgZn₂ formed in the welding seam using Zn and Zn–xAl filler metal. The tensile strengths of the joints increased with the increase of the matching degrees between the intermetallic compounds and the base metal when the welded seam contained different intermetallic compound. Meanwhile, the tensile strengths of the joints are decreased with the increase of intermetallic compound content when the welded seams contained the seam intermetallic compound.     

Identification of the intermetallic compound layer formed at the interface of roll-bonded aluminum-clad steel by thermal annealing

Aluminum clad steel (ACS) is an excellent layered composite material. An intensive investigation into roll-bonded ACS was carried out to identify the intermetallic compound (IMC) formed at the interface between the aluminum (Al) and the steel. A series of analyzing methods was applied to the IMC layer formed at the interface during annealing at 540 °C for 16 h. An electron probe micro-analyzer (EPMA) measured a value of 28.5 atomic percent for the Fe in the IMC layer, which coincided with the Fe₂Al₅ phase. An analysis of the X-ray diffraction pattern for the IMC layer in the ACS materials showed a very strong peak for the (002) plane of Fe₂Al₅. Vickers microhardness testing of the IMC layer revealed a very high value (1,110 Hv). The results of EPMA, XRD and microhardness values verified that the IMC layer in the sample that had been annealed at 540 °C for 16 h was the Fe₂Al₅ phase.     

铜对钢/铝激光-MIG复合焊接头组织及性能的影响

采用激光-MIG复合焊方法研究了铜对SYG960E超高强度度钢/6061铝合金焊接接头微观组织及力学性能的影响.结果表明,与MIG焊相比,激光-MIG复合焊有利于改善焊缝成形及焊接质量.钢/铝界面层具有双层结构,靠近铝焊缝侧为针状的FeAl₃金属间化合物,而靠近钢母材侧为条状的Fe₂Al₅金属间化合物.铜对钢/铝界面层及接头的力学性能具有显著的影响.添加铜后可以有效地减小界面层厚度和裂纹敏感性,降低钢/铝接头的最高硬度,明显提高接头的抗拉强度,接头强度可以提高110%,这主要与铜抑制界面层生长和改善界面层中Fe-Al金属化合物的脆硬性有关.     

Tensile resistance,microstructures of intermetallic compounds,and fracture modes of welded steel/aluminum joints produced using laser lap welding

The joining of DP780 steel to Al5052 was conducted by laser lap welding, in which the metal vapor and spatters were monitored by a high-speed camera. A universal testing machine was used to test the mechanical properties of the welded joints, and the changing law of lap tensile resistance with the laser welding parameters was analyzed. Optical microscope and scanning electron microscope were used to observe the macro-structure and micro-structure, respectively. Three different intermetallic compounds (IMCs) phases, i.e. banded Fe₂Al₅, FeAl₂ and needle-like FeAl₃ were generated at the steel/Al interface on microscopic observation. The aim of this research is to investigate the relationship among the lap tensile resistance, the welding parameters and the failure mode under different energy densities. Experimental results showed that the steel/Al joints have two different fracture modes at low heat input and high heat input. The failures happened along the heat-affected zone of the weld and along the steel/Al joint interface, respectively. And both of the two failure modes are brittle fractures. Additionally, cracks appeared at the fracture interface, and needle-like particle clusters were found in the fracture microstructure.     

Combination Effects of Nocolok Flux with Ni Powder on Properties and Microstructures of Aluminum-Stainless Steel TIG Welding-Brazing Joint

A flux consisting of Nocolok and nickel powder was first applied for TIG welding-brazing of aluminum-stainless steel. Results of tensile and impact tests illustrated that a significant improvement in mechanical properties of the butt joint was obtained with the flux, tensile strength increased from 116 to 158 MPa, and impact energy increased from 3.2 to 6.7 J. Investigation results on microstructures of interfaces and seams suggested that Ni addition significantly decreased the thickness of intermetallic compound (IMC) layer on the interfaces, but did not change the phase structure of Al₁₃Fe₄. Furthermore, precipitate phase in the welded seams changed from Al₆Fe to Al₉FeNi, and the quantity of precipitate phases decreased from 12 to 9% approximately. Finally, effect of Ni powder’s addition on the joint was analyzed and discussed. The reduction in the thickness of IMC and quantity of precipitate phases are beneficial to joint properties.     

Phase Relationships in the Zn-Rich Corner of the Zn-Fe-Zr System

The phase relationships in the Zn-rich corner of the Zn-Fe-Zr system at 450, 600 and 800 °C were investigated by means of x-ray powder diffraction (XRD) and scanning electron microscopy coupled with energy/wave dispersive spectroscopy (SEM-EDS/WDS). Two ternary compounds were found in the system. One of them was designated as ZrFe₂Zn₂₀ according its narrow composition range. It is a CeCr₂Al₂₀-type compound with lattice parameter a = 1.3941 nm. ZrFe₂Zn₂₀ is stable below 878.6 °C and can co-exist with all binary compounds in the Zn rich corner of the system. The other one was designated as Zr₂Fe₃Zn₅. SEM-WDS analysis indicated that Fe was hardly detected in ZrZn₂₂, Zr₅Zn₃₉ and ZrZn₃. And no Zr was dissolved in all Fe-Zn intermetallic compounds.     

Mg-Zn-Al三元系富镁角335°C等温截面(英文)

采用平衡合金法,利用X射线衍射、扫描电镜及能谱分析,系统地研究了Mg-Zn-Al三元系富镁角335°C的平衡相组成及其成分。从实验上证实,α-Mg固溶体并不与Mg32(Al,Zn)49(τ)三元金属间化合物或q准晶相平衡,而仅与一个三元化合物Al5Mg11Zn4(φ)相平衡。获得了φ相在335°C的整个成分范围,即:52.5%~56.4%Mg、13.6%~24.0%Al、19.6%~33.9%Zn(摩尔分数)。Al在Mg Zn相中的固溶度远大于在Mg7Zn3相中的固溶度,其最大值可达8.6%Al(摩尔分数)。Al和Zn可以同时固溶在α-Mg固溶体中。     

Surface Microstructure of Fe3Al After Severe Plastic Deformation

Nanocrystals were produced on the surface of Fe₃Al intermetallic compound by a severe plastic deformation technology—surface mechanical attrition. The phase and grain evolutions were characterized through x-ray diffraction technology, transmission electron microscopy, and Mossbauer spectroscopy. The results show that surface grains are refined to 15 nm in average size after 60 min of attrition. The surface grains present inhomogeneity due to the nonuniform plastic deformation when the attrition time is less than 15 min. Large quantities of dislocations and tangles of dislocations are observed in those larger grains. Al₈Cr₅ phase forms on the surface of Fe₃Al samples which have undergone attrition for less than 15 min. When the attrition time increases, the Al₈Cr₅ phase becomes disordered and dissolves into the matrix. In addition, disordering of Fe₃Al occurs only in a very thin area during severe plastic deformation.     

Formation of Al/(Al<Subscript>13</Subscript>Fe<Subscript>4</Subscript> + Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) Nano-composites via Mechanical Alloying and Friction Stir Processing

Combination of mechanical alloying and friction stir processing was used for the fabrication of Al/(Al₁₃Fe₄ + Al₂O₃) nano-composites. Pre-milled hematite + Al powder mixture was introduced into the stir zone generated on 1050 aluminum alloy sheet by friction stir processing. Uniform and active milled powder mixture reacted with plasticized aluminum to produced Al₁₃Fe₄ + Al₂O₃ particles. Al₁₃Fe₄ intermetallic showed elliptical shape with a typical size of ~ 100 nm, while nano-sized Al₂O₃ exhibited irregular floc-shaped particles that formed clusters with the remnant of iron oxide particles in the fine recrystallized aluminum matrix. As the milling time (1-3 h) of the introduced powder mixture increased, the volume fraction of Al₁₃Fe₄ + Al₂O₃ particles increased in the fabricated composite. The hardness and ultimate tensile strength of the fabricated nano-composites varied from 54.5 to 75 HV and 139 to 159 MPa, respectively; these are much higher than those of the friction stir processed base alloy (33 HV and 97 UTS). The highest hardness and strength were achieved for the nano-composite fabricated using the 3-h milled powder mixture; hard nano-sized reaction products and fine recrystallized grains of Al matrix had major and minor roles on enhancing these properties, respectively.