The mechanical mismatch effect frequently occurs in the dissimilar materials welded joints, thus leading to plastic gradient at the interface between the weld and heat-affected zone(HAZ). In this work, the boron steel...The mechanical mismatch effect frequently occurs in the dissimilar materials welded joints, thus leading to plastic gradient at the interface between the weld and heat-affected zone(HAZ). In this work, the boron steel and Q235 steel were selected for laser tailor welding,which obtained boron/Q235 steel tailor-welded blanks(TWBs). The method of welding with synchronous thermal field(WSTF) was utilized to eliminate the mismatch effects in TWBs. The WSTF was employed to adjust cooling rates of welded joints, thereby intervening in the solidification behaviors and phase transition of the molten pool. Boron/Q235 steel was welded by laser under conventional and WSTF(300-600 ℃) conditions, respectively. The results show that the microstructure of weld and HAZ(boron) was adequately transitioned to ferrites and pearlites instead of abundant martensite by WSTF. Meanwhile, the discrepancy of microhardness and yield strength between various regions of welded joints was greatly reduced, and the overall plasticity of welded joints was enhanced by WSTF. It is indicated that WSTF can effectively contribute to reducing plastic gradient and achieving mechanical congruity in welded joints by restraining the generation of hardbrittle phase, which could significantly improve the formability of TWBs in subsequent hot stamping.展开更多
基金the Natural Science Foundation of Fujian Province(2021J01299)school-enterprise cooperation project supported by Shandong Hongao Automotive Lightweight Technology Co.,Ltd.
文摘The mechanical mismatch effect frequently occurs in the dissimilar materials welded joints, thus leading to plastic gradient at the interface between the weld and heat-affected zone(HAZ). In this work, the boron steel and Q235 steel were selected for laser tailor welding,which obtained boron/Q235 steel tailor-welded blanks(TWBs). The method of welding with synchronous thermal field(WSTF) was utilized to eliminate the mismatch effects in TWBs. The WSTF was employed to adjust cooling rates of welded joints, thereby intervening in the solidification behaviors and phase transition of the molten pool. Boron/Q235 steel was welded by laser under conventional and WSTF(300-600 ℃) conditions, respectively. The results show that the microstructure of weld and HAZ(boron) was adequately transitioned to ferrites and pearlites instead of abundant martensite by WSTF. Meanwhile, the discrepancy of microhardness and yield strength between various regions of welded joints was greatly reduced, and the overall plasticity of welded joints was enhanced by WSTF. It is indicated that WSTF can effectively contribute to reducing plastic gradient and achieving mechanical congruity in welded joints by restraining the generation of hardbrittle phase, which could significantly improve the formability of TWBs in subsequent hot stamping.
文摘目的 了解某汽车零部件制造企业的工人听力健康现状,探讨听力损失的可能影响因素。方法检测个体接触噪声强度;测量个人声衰减值(personal attenuation rating,PAR);开展双耳6个频段(0.5~6.0 kHz)的气导纯音听阈测试;并使用问卷开展作业人员噪声接触情况和护听器使用情况调查。采用χ^(2)检验分析不同特征分组人群的听力损失发生率,构建logistic回归模型分析听力损失的影响因素。结果共调查某汽车零部件制造企业的281名噪声作业工人,个体接触噪声强度(normalization of equivalent continuous A-weighted sound pressure level to a nominal 8h working day,L_(EX,8h))范围为80.1~94.5 dB(A)。分析不同使用情况分组的工人之间的基线PAR,发现有无接受培训、是否知道正确佩戴方法、日常是否正确佩戴的工人的基线PAR比较,差异无统计学意义(P>0.05)。基线PAR未通过测试有35人,未通过率为12.4%。高频听阈提高检出55人,检出率为19.6%。男性工人年龄≥30岁、工龄≥10年、佩戴护听器后的噪声接触水平≥80 dB(A)的工人高频听阈提高发生较高(χ^(2)=3.064、17.103、2.933,P<0.1);工龄≥10年发生高频听阈提高的风险是工龄<10年者的4.224倍(OR=4.224,95%CI:1.920~9.297,P<0.01)。结论工龄是汽车零部件制造业工人听力健康的影响因素,部分工人佩戴护听器的防护效果不佳,部分工人高估了自己使用护听器的能力,企业应进一步加强培训。
