Corrosion properties of laser beam joints of aluminium with zinc-coated steel

This paper presents results of accelerated corrosion tests in a salt spray chamber as well as microelectrochemical measurements of thermally joint steel-aluminium mixed materials. The focus was set on analysing the corrosion behaviour of the different metallic materials (brazed seam, intermetallic phases, aluminium and steel sheet) in or within the vicinity of the brazed seam.Both corrosion tests show that the joining zone has the most negative corrosion potential and is the first to corrode. The degree of corrosive deterioration depends on the cathodic behaviour of the adjacent metal. Next to effective cathodes, such as steel or Fe-containing intermetallics, the attack is the most. However, contact to an aluminium alloy (AA6016) with its insulating oxide layer does not affect the corrosion properties of the respective filler materials.     

Joining phenomena and joint strength of friction welded joint between pure aluminium and low carbon steel

Abstract

This paper describes the joining phenomena and joint strength of friction welded joints between pure aluminium (P-Al) and low carbon steel friction welds. When the joint was made at a friction pressure of 30 MPa with a friction speed of 27·5 s^?1, the upsetting (deformation) occurred at the P-Al base metal. P-Al transferred to the half radius region of the weld interface on the low carbon steel side, and then it transferred toward the entire weld interface. When the joint was made at a friction time of 0·9 s, i.e. just after the initial peak of the friction torque, it had ～93% joint efficiency and fractured on the P-Al side. This joint had no intermetallic compound at the weld interface. Then, the joint efficiency slightly decreased with increasing friction time. The joint had a small amount of intermetallic compound at the peripheral region of the weld interface when it was made at a friction time of 2·0 s. When the joint was made at a friction time of 0·9 s, the joint efficiency decreased with increasing forge pressure, and all joints were fractured at the P-Al side. Although the joint by forge pressure of 90 MPa had hardly softened region, it had ～83% joint efficiency. To clarify the fact of decreasing joint efficiency, the tensile strength of the P-Al base metal at room temperature was investigated, and the tensile test was carried out after various compression stresses and temperatures. The tensile strength of the P-Al base metal has decreased with increasing compression stress at any temperature. Hence, the fact that the joint did not achieve 100% joint efficiency was due to the decrease in the tensile strength of the P-Al base metal by the Bauschinger effect. To obtain higher joint efficiency and fracture on the P-Al side, the joint should be made without higher forge pressure, and with the friction time at which the friction torque reaches the initial peak.     

riction welding of aluminium and plain low carbon steel

Synopsis

The effect of vanadium, in the range 5 to 1000 ppm, on the microstructure and properties of manual metal arc welds containing 0.6 to 1.8 % Mn has been investigated. It was found that vanadium increased the acicularity of as‐deposited metal and modified the grain size and the microphases in reheated regions. The hardness of the weldments increased and the tensile properties were defined by equations of the form:

σ =a+b.Mn+c.V‐d.V²

In the as‐welded condition vanadium was found, in some instances, to be marginally beneficial for notch toughness whereas after stress‐relieving the element had a progressively deleterious effect at all manganese levels. On balance, it is concluded, for the associated titanium content, that up to 200 ppm V can be tolerated without undue concern.     

Dissimilar metal joining of aluminium to zinc-coated steel by ultrasonic plus resistance spot welding – microstructure and mechanical properties

Vehicle body structures are increasingly utilising multi-materials designs with advanced high strength steels (AHSS) and aluminium alloys. A robust process for joining aluminium alloys to AHSS based on resistance spot welding (RSW) is essential to widespread application of such bi-metallic structures in fuel-efficient vehicles. In this study, ultrasonic plus RSW was applied to join AA6022 to Zn-coated dual-phase steel DP980. During solid-state ultrasonic spot welding, an interface structure comprising multilayer, Al–Zn and Zn–Fe intermetallics formed due to alloying of aluminium with steel coating. Such structure was subsequently melted into the aluminium nugget, and new Al–Fe intermetallics formed during RSW. Ultrasonic plus resistance spot-welded joints had superior fracture energy than direct resistance spot-welded joints.     

Nitriding of austenitic stainless steel using pulsed low energy Ion implantation

Using a pulse low energy ion implantation with an electronic beam switch operating in the kHz regime, a more efficient nitriding process is possible than with either pulsed plasma immersion ion implantation (PIII) or continuous low energy ion implantation (LEII). Besides the pulsed mode, a fast and precise external heating system for controlling the substrate temperature is necessary. Using such an experimental setup, it is shown that the duty cycle itself does not influence the diffusion and phase formation, as long as the exact same substrate temperature is maintained, thus nitrogen uptake and diffusion are decoupled. Optimal nitriding efficiency was observed for a duty cycle between 20 and 35%. At lower duty cycles (below 15% duty cycle), not enough nitrogen was available to allow the formation of expanded austenite, while higher duty cycles led to a reduced layer thickness caused by higher sputtering induced by the increased ion bombardment itself.     

Joining of high strength steel and aluminium alloy sheets by mechanical clinching with dies for control of metal flow

High strength steel and aluminium alloy sheets were joined by mechanical clinching with dies for control of metal flow. Since the sheets undergo plastic deformation for the joining during the mechanical clinching, the high strength steel sheets tend to fracture due to the small ductility. For the upper high strength steel sheet, fracture was caused by the concentration of deformation around the corner of the punch, and cracks were caused by the tensile stress generated in the bulged bottom into the groove of the die for the lower high strength steel sheet. To prevent these defects, metal flow of the sheets was controlled by optimising a shape of the die. For the upper high strength steel sheets, the depth of the die was decreased to prevent the concentration of deformation around the corner of the punch. On the other hand, the groove of the die was eliminated to reduce the tensile stress for the lower high strength steel sheets. The sheets below SPFC780 and SPFC980 were successively joined with the aluminium alloy sheet for the upper and lower high strength steel sheets, respectively.     

镀锌钢一6016铝合金异种金属加入中间夹层铅的激光焊接

对1．2mm厚镀锌钢板和1．15mm厚6016铝合金平板试件进行了加入中间夹层铅的激光搭接焊试验,通过调整焊接工艺参数获得最佳焊接成形,利用卧式金相显微镜、扫描电镜、x射线衍射、微机控制电子万能试验机等手段研究了焊接接头各区域的金相组织、断口形貌、主要物相与接头力学性能．结果表明,在钢／铝激光焊中添加中间夹层铅,焊接接...     

Welding aluminium alloys using low arc energy MIG method in terms of reducing pollutant emissions

Abstract

A comparison between the Charpy-V (CV) test, widely used in steel characterisation, and the dynamic fracture toughness K_1d found on precracked Charpy testpieces, is carried out.

The experimental procedure, not yet standardised, used to determine the dynamic fracture toughness K_1d (instrumented precracked charpy test or IPC test) is first described.

The experimental procedure, not yet standardised, used to determine the dynamic fracture toughness K_1d (instrumented precracked charpy test or IPC test) is first described.

The conceptual differences between dynamic fracture toughness K_1d and CV impact strength, the limits of CV testing in evaluating the toughness of steels, and finally the advantages of adopting the IPC test and its possible applications in the field of welding are then successively discussed.     

H13钢低温等离子体渗硼层的热熔损性能

研究喷丸预处理的H13钢低温等离子体渗硼试样的耐铝合金热熔损的性能.结果表明,经喷丸预处理的H13钢试样在590℃等离子渗硼2 h后,表面获得高硬度的硼化物层,其硬度值达10 GPa,厚度约为2 μm.通过动态热熔损实验,发现低温渗硼试样耐铝合金热熔损性能明显优于原始试样,并且当熔损时间较短时其耐热熔损效果尤其突出.     

Resistance spot welding of steel and aluminium sheet using insert metal sheet

Abstract

The present paper reports the resistance spot welding of steel and aluminium sheets using aluminium clad steel sheets as insert metals. Intermetallic compound layers were formed in the weld zones in direct spot welding of steel sheets to aluminium sheets. Thus, the strength of these joints was lower than that of aluminium to aluminium joints. Intermetallic compound layers were also formed at the steel/aluminium interfaces of the insert metal in welding of steel to aluminium using an insert metal sheet. However, the strength of these joints was of the same order as that of the aluminium joints. The fracture mode of these joints varied with the welding current. The suitable welding current for steel to aluminium joints varied between the values suitable for steel to steel and aluminium to aluminium joints. The fatigue strength of joints using insert metals was somewhat lower than that of the aluminium joints.     

316L不锈钢的低能量激光冲击强化工艺

以316L不锈钢作为模型材料,系统研究了低能量高重频激光冲击强化工艺。建立了激光光斑覆盖率概念,对于直径d为0.4~0.8 mm 间的光斑,其饱和覆盖率在6~7之间。在此饱和覆盖率条件下,机械手移动速率v与光斑直径d的匹配关系为v=70d。最大残余压应力随着光斑直径的减小而增大,当光斑直径d为0.4 mm时获得最大残余压应力为662 MPa,残余压应力影响层深度为565 μm。激光冲击强化区域表面粗糙度未明显增加,但与未冲击区域存在一定高度台阶。在1.59 GW/cm²激光功率密度下,该台阶高度为23 μm。     

Al元素对高强钢药芯焊丝焊缝金属组织和性能的影响

采用自行研制的高强钢药芯焊丝焊接Q960钢,通过改变药芯成分中Al元素的含量获得了含有不同Al元素的焊缝金属。利用拉伸试验、不同温度下冲击试验对焊缝金属的强度和韧性进行了测试;结合金相组织、扫描电镜观察等手段分析了Al元素对焊缝金属组织和性能的影响机理。结果表明：焊缝金属中Al元素含量的变化对接头抗拉强度和断后伸长率影响不大,但对焊缝金属冲击吸收能量影响较大。随着Al元素含量的增加,冲击吸收能量呈现先增大后降低的趋势。当Al元素含量较低时,易生成Al2O3氧化物,针状铁素体易形核和长大,有利于提高焊缝金属冲击吸收能量;当Al元素含量较高时,易生成AlN氮化物,同时组织中存在着δ-铁素体组织,造成焊缝金属冲击能量降低。     

冷速对不同Ni含量低温钢的组织及相变的影响

采用热力模拟试验机研究了Ni含量为0.20%、0.50%、0.80%3种成分低温试验钢T1、T2、T3在不同冷却速率下的组织转变规律及其CCT曲线,采用光学显微镜对组织进行了观察,采用显微硬度计对其硬度进行了测定,分析了Ni含量及冷却速率对显微组织和硬度的影响。结果显示,随Ni含量增加,试验钢的铁素体转变区域、珠光体转变区域逐渐减小,T1试验钢铁素体转变温度范围为739~465℃,珠光体转变温度范围为659~558℃,T2试验钢铁素体转变温度范围为716~509℃,珠光体转变温度范围为644~574℃,T3试验钢铁素体转变温度范围为690~500℃,珠光体转变温度范围为572~513℃。当冷速为10℃/s,V析出强化作用开始减弱,此时硬度值出现一个波谷。控制合理冷速在5~10℃/s之间,Ni含量控制在0.50%~0.80%之间,有利于韧性相针状铁素体、贝氏体复相组织生成。     

双电源低温渗氮工艺在316不锈钢上的应用

通过正交试验研究了交流脉冲电压、直流脉冲偏压和温度对316不锈钢表面硬度和渗层厚度的影响,获得了双电源低温渗氮最佳工艺参数。通过光学显微镜(OM)、X射线衍射仪(XRD)、显微硬度计、电化学工作站以及摩擦磨损试验机等研究了最佳工艺下渗氮试样的性能。结果表明,影响渗氮试样性能因素的顺序为:交流脉冲电压＞温度＞直流脉冲偏压。最佳工艺参数为交流脉冲电压360 V,直流脉冲偏压270 V,温度380 ℃。对最佳工艺制备的试样与单电源进行对比:渗层厚度为43.4 μm,是单电源的8.5倍;表面硬度为1350 HV0.025,是单电源的3.1倍;自腐蚀电位由－256 mV(vs SCE,下同)提高到－180 mV;自腐蚀电流密度从13.90 μA/cm² 降低到0.45 μA/cm²;摩擦因数从0.55降低到0.42。双电源渗氮速率的提高是由于高能离子轰击引起的表面结构缺陷和渗氮气体的高度离解。     

合金元素对低合金耐磨钢组织及性能的影响

对不同合金元素含量的低合金耐磨钢进行淬火加回火热处理后,测试力学性能及－40 ℃冲击吸收能量,借助SEM、TEM等分析组织及析出相,研究合金元素对低合金耐磨钢的组织和性能的影响。结果表明：含有Ni、Cu、Cr、Mo等合金元素的试验钢淬火及190 ℃低温回火后均得到板条状马氏体组织,马氏体板条间有细小碳化物析出相。而没有添加Ni、Cu及少量添加Cr、Mo元素的试验钢淬透性降低,淬火及低温回火组织为马氏体及少量铁素体。添加Ni、Cu、Cr、Mo等合金元素的试验钢淬火及低温回火后得到较好的综合力学性能,最佳性能为屈服强度1218 MPa,抗拉强度1507 MPa,硬度429.5 HV,－40 ℃冲击吸收能量27.7 J。     

Simulation and measurement of aluminium–nitride precipitation in hot rolled Al killed low carbon steel coil

Abstract

Aluminium–nitride precipitation is of great importance in the deep drawability of Al killed low carbon steels. The industrial processing of Al killed steel has some critical points at which the drawability of the final product is strongly influenced by the processing parameters (hot rolling end temperature, coiling temperature). The nitrides are dissolved at the slab reheating temperature (1250°C), and most of the nitrogen remains in solid solution until the hot rolling finishes. The precipitation of nitrides in ferrite occurs more quickly than in austenite, consequently the coiling temperature must be enough low to keep the nitrogen in solid solution. The main purpose of this paper is to describe the aluminium–nitride precipitation process in hot rolled coil. Moreover, on the basis of a phenomenological model of the precipitation process the precipitated fraction of nitrides coiling has been calculated.     

Self-piercing riveting of high tensile strength steel and aluminium alloy sheets using conventional rivet and die

High tensile strength steel sheets having different strengths were joined with an aluminium alloy sheet by a self-piercing rivet. In the joining, a conventional rivet and die used for aluminium alloy sheets were employed in order to have the versatility for various steel sheets. The effects of the flow stress of the high strength steel sheets and the combination of the sheets on the joinability of the sheets were investigated by finite element simulation and an experiment. As the tensile strength of the high strength steel sheet increases, the interlock for the upper high strength steel sheet increases due to the increase in flaring during the driving through the upper sheet, whereas that for the lower high strength steel sheet decreases. The joint strength for the lower high strength steel is comparatively smaller than that for the upper high strength steel sheet. It was found that the high tensile strength steel sheets below 590 MPa were fully joined with the aluminium alloy sheet even with the conventional self-piercing rivet and die.