Effect of plastic deformation on the properties of VAD15 forging aluminium alloy and welded joints in this alloy

The results are presented of the investigations of the effect of the surfacing parameters on the penetration area and thermal efficiency in the conditions of constant heat input in automatic deposition of a bead on a thick component. The correction coefficients for calculating the penetration area using the well-known and corrected Rykalin equation for a constantly acting and rapidly moving point heat source on the surface of the thick component are determined.     

Effect of heat input on weld bead geometry of submerged arc welded ASTM A709 Grade 50 steel joints

A series of measurements was carried out on specimens of submerged arc welded plates of ASTM A709 Grade 50 steel to determine how variation in heat input achieved using single and double wires affected bead reinforcement, bead width, penetration depth, contact angle, heat affected zone (HAZ) size, deposition area, penetration area and total molten area. The level of dilution and different melting efficiencies were calculated and their variation with heat input was analyzed based on the acquired measurements. The cooling time from 800 to 500 °C was also related to various weld bead characteristics (e.g., total nugget area, heat transfer boundary lengths, bead width-to-depth ratio, and nugget parameter). The bead reinforcement, bead width, penetration depth, HAZ size, deposition area and penetration area increased with increasing heat input, but the bead contact angle decreased with it. The electrode melting efficiency increased initially and then decreased with increasing heat input, but the plate melting efficiency and percentage dilution changed only slightly with it. Cooling time exhibited a very good linear relationship with the total nugget area, heat transfer boundary length, and nugget parameter.     

On the resistance spot welding of four-sheet stack of unequal sheet thickness

There is a lack of sufficient understanding regarding resistance spot welding behaviour of multi-layer structure. This paper investigates the weld nugget development and failure characteristics of four-sheet joint of dissimilar sheet thickness (0.7/1.2/1.2/0.9?mm) made on low carbon steel. The heat dissipation via water-cooled electrode hinders the weld nugget penetration into the thin/thick sheet interface. It was shown that increasing heat input led to bonding mechanism transition from solid-state welding to fusion welding at thin/thick sheet interface. Increasing welding current beyond a critical value changed the failure mode from interfacial to pullout leading to improvement of energy absorption of the joint. Fusion zone size along middle sheet/sheet interface proved to be the most important controlling factor for mechanical properties of four-sheet resistance spot welds.     

Experimental study on welding characteristics of CO2 laser TIG hybrid welding process

Abstract

The experiments of CO₂ laser TIG paraxial hybrid welding with 4 mm thick AISI 321 stainless steel sheet have been performed. The arc images and welding characteristics have been investigated with different energy ratios between laser and arc. The experimental results indicate that the hybrid welding is similar to laser welding and has also two welding mechanisms: deep penetration welding and heat conduction welding. Because of the effect of keyhole induced by laser, the arc root can be stabilised and compressed, and the current density and the penetration depth are all increased significantly, which show the characteristics of deep penetration welding. However, when the current is increased to a critical value, the laser induced keyhole disappears and the arc expands obviously, which decreases the penetration depth, so that the welding mechanism has been changed from deep penetration welding to heat conduction welding. Furthermore, the effects of distance between laser beam and electrode, pulsed laser and hybrid manners on hybrid welding characteristics have also been studied.     

醇基防渗透砂状涂料替代锆英粉涂料的研究应用

介绍了一种用于铸钢件的可替代锆英粉涂料的新型醇基砂状涂料,耐火骨料采用以70～200目为主的铬铝质砂状材料。这种涂料有着良好的悬浮稳定性,涂刷流畅,多次反复涂刷不起皮,附着强度高,发气量小。它与高温钢液接触时,有着很高的热稳定性,不与FeO等金属氧化物起熔蚀反应,抗钢液渗透能力强。在许多铸造厂应用表明:其防渗透粘砂效果优于锆英粉涂料。当涂刷达到5～6遍,可以部分替代铬铁矿面砂工艺而应用于厚大铸钢件热节处。     

调角器总成激光穿透焊工艺研究

激光焊工艺能量密度高、精度高、热影响区和焊接变形小,适用于汽车精密零部件的焊接。针对座椅调角器与3 mm厚连接板的连接,采用激光穿透焊替代电弧焊,结构上无需预留工艺开口,产品设计更加柔性化;调整激光焊接的工艺参数,分析各工艺参数对焊接质量的影响,当激光功率为2200 W、焊接速度为20 mm/s、负离焦量为5 mm时,可获得较好的焊缝外观质量,在满足多条焊缝紧密布置的同时,其焊接熔深达到3.9 mm以上。     

锥裙锁表面疑似裂纹磁痕显示原因分析

飞机机尾罩与机体连接用ZG0Cr14Ni5Mo2Cu不锈钢锥裙锁铸钢件，在磁粉检测时，其表面有多条疑似裂纹状线性磁痕显示，后采用荧光渗透检测方法进行辅助检测，原磁痕显示处未见异常荧光显示。采用表面形态?组织特点?成分分布?磁性变化相结合的研究思路，开展表面形态电镜观察、显示区剖面金相检查、组织微区成分能谱分析、材料硬度测试、XRD相分析以及模拟热处理等试验。结果表明:锥裙锁磁痕显示区未见表面缺陷，铸钢的枝晶间存在较粗大条状分布的残余奥氏体组织，这种组织差异破坏了材料磁性的连续性，导致其表面出现磁痕显示；锥裙锁宏微观组织不均匀，存在奥氏体富集区，其产生与C、S、P类元素偏析有关，研究为该材料零件在磁粉检测时的磁痕判定提供了依据和借鉴。     

Development of narrow gap multi-layer welding process using oscillation laser beam

The oscillation laser beam is considered to be effective as a heat source of narrow gap multi-layer welding because oscillation laser welding can control the penetration shape and prevent the lack of fusion. In this study, in order to establish a narrow gap welding process by oscillation laser beam, butt welding experiments of 50 mm thickness carbon steel plate were performed. By the appropriate control of the heat input area using the in-process sensor for recognizing the groove shape, narrow gap welding of a thick plate with groove which was cut by gas cutting was achieved. Properties of the welded joint had been confirmed by nondestructive testing, tensile test and side bend test. A two-dimensional numerical calculation model for welding deformation was developed. This calculation model was used for investigation of the optimal groove angle. The results of calculations were in quantitative agreement with the experimental results. Microstructure of the weld zone had multiple thermal histories. According to the hardness test results, maximum hardness of the heat affected zone of the upper layer has been lowered than that of the lower layer.     

Plasma spraying of self-fluxing alloys with a remote arc with melting of the coating

One of the most advanced and efficient methods of increasing the service life of machine components and mechanisms is the deposition of hardening coatings on the working surfaces. The coatings of nickel-based self-fluxing alloys deposited by plasma spraying are used widely in various branches of engineering. The properties and bonding strength of plasma coatings produced from nickel-based self-fluxing alloys can be improved by melting the surface layer at a specific temperature. In this work, the authors propose a method of calculating the depth of penetration in spraying the coatings of self-fluxing alloys with a remote arc taking into account the changes of the heat conductivity of the material which depends on porosity and temperature. The experimental results are used to determine the values of the heat conductivity coefficient for the nickel-based self-fluxing alloys. The dependence can be used for the more accurate selection of the power of the remote arc. The difference between the calculated and experimental values is smaller than 10%.     

基于改进热源模型的铝合金MIG焊数值分析

采用CMOS高速摄像机检测和分析铝合金熔化极气体保护焊(MIG焊)熔滴过渡行为,确定MIG焊熔滴的过渡频率和速度.在理论分析MIG焊热源特性、热作用模式以及焊缝形貌前提下,从宏观焊接热过程出发,提出并开发了适用于MIG焊的组合体积热源分布模式,MIG焊电弧被处理描述为经典的双椭球体热源模型,熔滴能量作用模式被表示成均匀球体热源模型.同时,在均匀球体热源模型中加入了熔滴热能和动能,实现了熔滴对MIG焊熔池冲击作用的影响.基于上述热源模型,建立了铝合金MIG焊温度场有限元模型,对厚板铝合金MIG焊温度场进行了模拟.结果表明,模拟获取的焊缝熔合线走势及形貌和实际焊接结果相吻合,证明开发的热源模型能够准确描述MIG焊指状熔深特性和热传导过程.