Creep and tensile properties of press molding joined GMT-sheets

GMT-sheet is used in automobile bumper with high rigidity and strength, and its joining strength is influenced by lap length, one of the joined molding conditions. Fracture strength was calculated by dividing fracture load with cross-sectional area. Total five repeated measurements were made to obtain the average value. Tensile test was conducted at room temperature for 10 specimens. In addition, the effect of compression ratio on creep and tensile performance during lap joined molding was discussed. With increasing lap length, the lap joining efficiency of GMT-sheet was increased. However, higher compression ratio reduced the joining efficiency. Creep test on GMT-sheet showed abrupt fracture without tertiary creep. This can be explained by the weak thermal resistance of the resin. If GMT-sheet was exposed to high temperature for a long time, it was easily failed by external force.     

实心铆钉铆接与螺栓连接强度对比试验研究

采用螺栓连接、实心铆钉铆接两种连接方式对钢板进行连接试验。对实心铆钉铆接进行了有限元数值模拟,得出合理的铆钉高度。对螺栓连接件与实心铆钉铆接件进行板料搭接及对接结构拉伸强度测试,结果表明:螺栓连接件的抗剪强度略大于实心铆钉铆接件的抗剪强度,螺栓连接件的抗剥离强度明显大于实心铆钉铆接件的抗剥离强度。     

铝合金/碳钢药芯焊丝熔-钎焊时的界面层脱落(英文)

采用锌基药芯焊丝对铝合金和无镀层低碳钢进行钨极氩弧熔-钎焊搭接。在焊缝中发现从界面层脱落的富铁层,Al-Zn相流入界面层和脱落层之间的夹层区域,并加速富铁层的进一步脱落。在焊缝凝固过程中,富铁脱落层逐渐向焊缝深处扩散、迁移。界面层的厚度为15μm,焊态下铝/钢异种金属接头的抗拉强度达111MPa。经焊后热处理,接头的抗拉强度提高到150MPa。     

Effect of nickel coating on the shear strength of FSW lap joint between Ni–Cu alloy and steel

Cu–Ni alloy and low-carbon steel were joined by friction stir lap welding (FSLW) with the help of a nickel coating. The appropriate welding parameters were investigated and the lap joints were analyzed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and shear strength testing. The shear strength of joints with a nickel coating was about 2.9 times as high as that of the joints without Ni coating. According to the EDS analysis of the fractured surfaces under the shear strength test, the micro-voids occurred in the Cu–Ni/steel interface without Ni coating, thus reducing the shear strength. These micro-voids were reduced in size using a nickel coating due to the self-diffusion in the Ni/Ni interface at high interface temperature and high contact pressure. The strong bonding mechanism using a nickel coating could be explained by the iron and copper atoms diffusing into the coating through the interface at high interface temperature and holding time.     

Resistance welding of carbon fibre reinforced polyetheretherketone composites using metal mesh and PEI film

Weldability of polyetheretherketone( PEEK) with polyetherimide( PEI) is tested. And carbon fiber reinforced PEEK laminates are resistance welded using stainless steel mesh heating element. The effects of the welding time and welding pressure on the lap shear strength of joints are investigated. Results show that PEEK can heal with PEI well in welding condition and the lap shear strength of PEEK/CF(carbon fibre) joint increases linearly with welding time, but reaches a maximum value when welding pressure ranging from 0.3 MPa to 0.5 MPa with constant welding time. The fracture characteristics of surface are analyzed by SEM techniques, and four types of fracture modes of lap shear joints are suggested.     

Resistance spot welding of metal/carbon-fibre-reinforced plastics and applying silane coupling treatment

Dissimilar materials joining of SUS304 and carbon-fibre-reinforced plastics consisting of short fibres and thermoplastics was performed. The materials were joined by series resistance spot welding. The electrodes were pressed on the metal plate of the lap joint of metal/carbon-fibre-reinforced plastics. The SUS304 plate was heated by resistance heating, causing the thermoplastic near the interface to melt slightly because of heat conduction. SUS304 could be joined directly to carbon-fibre-reinforced polyamide and modified polypropylene, but not to polyphenylene sulphide. The joining area increased with an increase in the welding current and welding time, so did the tensile shear fracture load. Furthermore, the silane coupling agent treatment of SUS304 was highly effective in increasing the joining strength.     

Fluxless joining of aluminium alloy to steel by laser irradiation method

A6061 aluminium alloy was joined with steel using Zn filler metal under laser irradiation process. The quality of joint was evaluated by the strength of a lap joint. The effects of laser power irradiation conditions such as travelling speed and defocused distance on the joint strength were investigated. The maximum joint strength was obtained at relatively medium laser travelling speed. The excess reaction between filler metal and aluminium formed thick brittle intermetallic compounds between steel and aluminium alloy. The compounds are considered to lead to the reduction in joint strength. It was found that low wetting at high travelling speed and excess reaction layer formation at low travelling speed were responsible for low joint strength. The study revealed that the relatively high joint strength between aluminium alloy and steel was obtained by laser joining method using Zn filler without the use of flux in air atmosphere.     

Effect of plasma electrolytic oxidation coating on joining metal to plastic

Abstract

Joining of magnesium alloy to polyethylene without adhesive using a newly developed friction lap welding technology was investigated. The polyethylene and magnesium alloy were hard to be joined together without surface premodification due to the lack of polar groups on polyethylene surfaces. Strong hybrid joints were achieved after the polyethylene was treated by corona discharge, and the magnesium alloy was subjected to plasma electrolytic oxidation treatment. Scanning electron microscope and high resolution transmission electron microscope observations demonstrated that the high joining strength was attributed to the development of both chemical bonds at the interface and micromechanical interlocking.     

连接工艺对铝合金结构件力学性能的影响

对7B04铝合金回填式搅拌摩擦点焊及铆接连接的结构件的静力与疲劳性能进行对比测试. 结果表明,由铆接与回填式搅拌摩擦点焊连接的典型结构的压缩静力载荷在117 ~ 124 kN范围内波动,剪切静载荷波动范围为89 ~ 95 kN,焊点间距对载荷的影响较小;铆接连接的典型件剪切疲劳寿命低于回填式搅拌摩擦点焊结构件寿命. 对于点焊结构而言,接头微观组织不均匀导致硬度不均匀,同时搭接面处钩状结构向上弯曲,最终使得疲劳试件的失效主要沿轴肩回抽路径.     

汽缸体铸造生产中的子母芯控制技术

在造型中,下芯是一道很重要的工序,难度较大的是子母芯,保证芯子的强度和牢固固定是难点。笔者在多年的造型工作中,逐渐摸索出一套处理子母芯的方法,在生产中特别是生产哈汽342514汽缸体时,取得了较好的效果。本文着重介绍哈汽342514汽缸体生产过程中的子母芯控制技术。     

考虑残余应力的激光搭接焊接头拉伸和疲劳试样宽度标准化

抗剪强度和疲劳强度是激光搭接焊接头性能的两个最重要指标。关于激光搭接焊接头的拉伸和疲劳试样的宽度选取,目前还没有相应的标准进行规定。以不锈钢薄板激光搭接焊接头为研究对象,通过残余应力数值与试样宽度变化关系的测定,确定了考虑和不考虑残余应力影响的拉伸和疲劳试样合理宽度,比较了有无残余应力试样抗剪强度的区别。结果表明,残余应力通过改变焊接接头受力状态和微观变形均匀性降低了薄板激光搭接焊接试样的抗剪强度。     

Microstructural Evolution and Mechanical Behavior of Friction-Stir-Welded DP1180 Advanced Ultrahigh Strength Steel

Friction stir lap welding of a DP1180 advanced ultrahigh strength steel was successfully carried out by using three welding tools with different pin lengths. The effects of the welding heat input and material flow on the microstructure evolution of the joints were analyzed in detail. The relationship between pin length and mechanical properties of lap joints was studied. The results showed that the peak temperatures of all joints exceeded A c3, and martensite phases with similar morphologies were formed in the stir zones. These martensite retained good toughness due to the self-tempering effect. The formation of ferrite and tempered martensite was the main reason for the hardness reduction in heat-affected zone. The mechanical properties of the lap joints were determined by loading mode, features of lap interface and the joint defects. When the stir pin was inserted into the lower sheet with a depth of 0.4 mm, the lap joint exhibited the maximum tensile strength of 12.4 kN.     

Novel dissimilar spot welding of aluminium alloy and steel sheets by friction stirring

Friction stir spot welding (FSSW) has been applied to a dissimilar metal lap joint of an aluminium alloy and steel by stirring only the upper aluminium alloy sheet. Therefore, FSSW cannot be used to weld a lap joint composed of three or more sheets and a lap joint with an adhesive interlayer. In the present work, we propose a novel spot welding process for dissimilar metal lap joints using a new tool with the tip made of spherical ceramics. When this process is applied to the lap joint of the aluminium alloy and steel, the tool can be plunged into the lower steel sheet, then a steel projection is formed in the aluminium alloy sheet. The height of this steel projection increases with the plunge depth, and accordingly, the weld strength increases; the tensile shear strength and the cross tensile strength reached about 3.6 and 2.3 kN/point, respectively.     

Strengthening of spot-welded lap joints by new hardened zone

This paper deals with strengthening of spot-welded lap joints by a new hardened zone. Based on the equation to predict the strength proposed by past researchers, the factors necessary for strengthening were extracted. And, based on these factors, the strengthening of spot-welded lap joints was examined. First of all, in order to increase the hardened zone, the vicinity of the nugget edge was heated with a laser. Next, tensile shear tests were conducted by using spot-welded lap joints, which were heated by laser at various distances from the nugget. Finally, the relationship between tensile shear strength and the distance from the nugget centre to the crack was clarified. As a result, by increasing the hardened zone, we found that the fracture position was far away from the nugget edge. And, we found that the tensile shear strength could be improved by 15%.     

Effect of anodizing on direct joining properties of aluminium alloy and plastic sheets by friction lap joining

We have proposed a novel joining process, friction lap joining (FLJ), to join metallic material sheet directly to polymer sheet and have investigated mechanical and metallurgical properties of these dissimilar joints. The joining mechanism is discussed with an evaluation of the TEM microstructure at the joint interface between A2017 aluminium alloy and two kinds of polymer, ethylene-acrylic acid copolymer (EAA), and high density polyethylene (PE). EAA sheet was easily joined to an as-received aluminium alloy sheet by FLJ, because EAA had a polar functional group, COOH. On the contrary, PE was not able to be joined to an as-received aluminium alloy, because PE had no polar functional group. However, anodizing of aluminium alloy was effective to join these materials by the assistance of the anchor effect.     

汽车前地板后本体复合模压成形工艺

针对汽车前地板后本体在线复合模压成形工艺,探究采用螺杆机混合浸润挤出的LFT-D高温坯料与单向碳纤维预浸料增强片的多元复合模压过程,通过正交实验法,研究复合模压成形的主要工艺参数(入模料温、模压压力、合模速度和保压时间等)对成形缺陷的影响,结合力学性能实验进行筛选,确定出了优化后的成形工艺组合参数为:单向碳纤维预浸料增...     

Microstructure,static and fatigue properties of refill friction stir spot welded 7075-T6 aluminium alloy using a modified tool

ABSTRACT

Defect-free joints were produced in 2.0?mm thick 7075-T6 Al alloy by refill friction stir spot welding using a modified tool. Weld performance was evaluated in terms of microstructure, interfacial bonding, hardness, static and fatigue strength based on the experimental observations. The results indicated that grain size, interfacial bonding quality and lap shear strength significantly depend on sleeve penetration depth (SPD), with sufficient interfacial bonding and stable lap shear strength achieved when SPD?≥?1.8?mm. The SPD and applied load played a dominant role in determining the static lap shear and fatigue failure mechanisms, respectively. More precisely, the lap shear failure mode was an interfacial failure when SPD?≤?1.8?mm, and nugget pullout when SPD?≥?2.0?mm. The fatigue fracture mode involved nugget pullout under high applied load, while fracture through the parent sheet occurs under medium and lower applied loads.     

Study on TIG welding of dissimilar Mg alloy and Cu with Fe as interlayer

Abstract

Dissimilar Mg alloy and Cu lap joints were prepared by tungsten inert gas (TIG) welding with Fe as an interlayer, without producing intermetallic compounds MgCu₂ and Mg₂Cu. Copper and Fe were joined together in the form of remelt deposit welding and Mg alloy and Fe plate were joined together in the form of brazing. During tensile testing, the joints between Fe plate and Mg alloy fractured, and Mg alloy and Fe plate were joined together by interatomic force. Metallic oxides produced in the interface between Mg and Fe resulted in reduction in the mechanical properties of the welded joints.     

Strengthening of cross tension strength of spot-welded lap joints by increasing the opening angle on the nugget edge

This paper deals with the strengthening of spot-welded lap joints by increasing the opening angle on the nugget edge. Based on the equation proposed by past researchers to predict the strength, the factor necessary for the strengthening was extracted. And, based on this factor, the strengthening of spot-welded lap joints was examined. First of all, in order to increase the opening angle on the nugget edge, the vicinity of the nugget edge was bent with a bending machine. Next, cross tension strength (CTS) tests were conducted into the spot-welded lap joints with various opening angles on the nugget edge. Finally, the relationship between CTS and the opening angels of the nugget edge was clarified. As a result, by increasing the opening angles on the nugget edge, we found that the CTS could be improved by 20%.     

不锈钢薄板大间隙接头激光-MIG电弧复合高速焊接工艺

采用填充ER316焊丝的光纤激光-MIG电弧复合焊方法,焊接间隙为0.5 mm、厚度为1 mm的SUS444铁素体不锈钢薄板对接接头和搭接接头,研究了获得成形良好的对接接头和搭接接头的工艺参数窗口和极限焊接速度,并对焊缝进行了着色渗透检验和拉伸试验. 结果表明,合理匹配焊接速度和焊接电流,是获得成形良好的大间隙接头的关键;当焊接速度过小或焊接电流过大时,较大的热输入导致焊缝过度熔透,焊缝成形不良;当焊接速度过大或焊接电流过小时,较小的热输入导致焊缝未熔透. 对接接头焊缝成形质量良好且熔透的极限焊接速度可达12 m/min,而搭接接头的极限焊接速度为5 m/min. 成形良好的焊缝均未发现表面裂纹. 拉伸试验表明,对接接头断裂在母材上;搭接接头绝大部分断裂在熔合线附近,极限焊接速度下获得的搭接接头的抗拉强度是母材的84.2%.