[Objective]The purpose is to study influence of welding process parameters on properties of spot welded joints of hot forming steel.[Methods]The orthogonal test is performed for 22MnB5 press-hardened steel.[Results]The order of priority affecting the mechanical properties of spot weld is welding current,electrode pressure and welding time under the condition of single pulse welding process.The best mechanical properties of the welded joint and the good welding quality can be gotten with the best welding parameters,welding current of 8.5 kA,welding time of 525 ms,and electrode pressure of 4 kN.[Conclusion]The press-hardened steel welded joint consists of the BM area,the tempering area,the softening area,the critical area and the nugget area.There is a serious stress concentration at the welding point joint line(nugget zone),which is a dangerous area for the failure of press-hardened steel welding joints.The last pulse small heat input can significantly reduce the stress concentration of the welding joint and improve the mechanical properties of the joint by using multiple pulse welding.
In this investigation, cast nickel aluminum bronze (NAB) was subjected to friction stir processing (FSP). The mechanical properties and the cavitation erosion behavior of the as-cast and FSP NAB alloy were investigated. The results showed that the initial microstructure of the as-cast NAB transformed to the fine and homogeneous microstructure after FSP, therefore improving the microhardness, yield strength, ultimate tensile strength, and elongation of as-cast NAB alloy. The cavitation erosion test showed that the FSP improved the cavitation erosion resistance of the as-cast NAB alloy in the distilled water. Furthermore, the cavitation erosion mechanisms in as-cast and FSP NAB alloy were investigated and understood in terms of schematic diagrams in this research.
通过焊接工艺、焊接结构的优化,对比研究复合板对接接头质量,采用金相分析、硬度测试、X射线能谱、断口分析等手段,研究了(Q345R + S30403)复合板根部焊接裂纹的成因.结果表明,焊缝成分发生明显改变是不锈钢母材对根部焊缝的稀释作用,显著增大了焊缝淬硬倾向,是导致焊接氢致延迟裂纹发生的根本原因.研究得出了复合板焊接裂纹的有效控制方法,5 mm钝边、单边V形坡口、无间隙组对等结构设计和背部清根处理、不锈钢背部盖面的焊接工艺,有效避免了根部焊接冷裂纹的发生.该研究对石油、化工、电建及压力容器等防腐结构件的焊接质量提升具有重要的工程指导意义.
通过焊接热模拟并结合有限元数值模拟,对X80 环焊缝同一区域进行多次返修模拟,研究不同次数返修后环焊缝的微观组织、韧性、硬度和承压能力的变化.结果表明,不同返修次数下,焊接接头组织类型未发生变化;多次返修对组织的影响具有叠加效应,焊接热输入的作用使晶粒发生再结晶细化,对韧性具有优化作用;但随着热循环的反复作用,细化后的晶粒又开始长大,并在 3 次返修后韧性发生劣化;焊缝返修使焊接接头的硬度显著下降并增大了硬度分布的分散性,多次返修能够在首次返修的基础上略微提高接头硬度;在内压条件下,返修后环焊缝的等效应力高值分布在填充焊焊层,且应力随返修次数的增加而增大;1 次返修使环焊缝承压能力下降明显,此后随着返修次数增加,承压能力降幅较小.综合考虑强韧性及承压能力,建议X80 管道环焊缝返修次数不超过 2 次.
采用 4004 钎料真空钎焊 6063 铝合金蜂窝板,研究了不同蜂窝芯厚度对钎焊接头微观组织的影响.结果表明,在钎焊温度为 585℃、保温时间为 20 min时,厚度为 0.10 mm蜂窝芯无法钎焊成形.3 种不同厚度蜂窝芯均有熔蚀现象产生.当单层蜂窝芯厚度为 0.10 mm和 0.15 mm时,在钎焊界面反应区存在白色的Al-Si共晶相,其形貌在单层窝芯厚度 0.10 mm时为块状,其形貌在单层窝芯厚度 0.15 mm时为树枝状;当单层蜂窝芯厚度为 0.21 mm时,白色的Al-Si共晶相消失,仅存在Si元素富集相.双层蜂窝芯厚度为 0.10 mm的蜂窝板钎焊界面坍塌;当双层蜂窝芯厚度为 0.15 mm时,界面反应区(富Si金属间化合物相)较大,但是芯材没有发生熔解现象,界面反应区与芯材之间也形成部分影响区(α-Al固溶体相),面板与界面反应区之间的影响区也小于双层蜂窝芯厚度为 0.10 mm的影响区;当双层蜂窝芯厚度达到 0.21 mm时,面板与界面反应区中间的影响区增大,芯材同样没有发生熔解现象,芯材界面反应区变小;即双层蜂窝芯脆性富Si金属间化合物减少,α-Al固溶体相增多.
