共查询到19条相似文献,搜索用时 359 毫秒
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《焊接技术》2016,(5)
采用CO_2激光-MIG复合焊对7A05铝合金进行了焊接工艺研究,研究了热源间距、焊接速度及MIG焊接电流对焊接气孔形成规律的影响。通过对焊缝进行X射线检测,进一步探讨了气孔的特征及其形成原因和控制方法。结果表明,焊缝中的气孔数量与板材的焊前处理状态、焊接保护效果及焊接工艺有着显著的联系。其中,冶金类气孔的形成机制是铝合金板材及焊接材料表面的水分分解出氢溶入到熔池中不能逸出,因而,通过加强焊前处理及减少熔池吸氢时间可有效控制冶金类气孔的形成;工艺类气孔的主要形成机制是激光深熔焊的"匙孔"坍塌,而通过优化激光-MIG复合焊接工艺及加强熔池背部保护也可较好地控制工艺类气孔的形成。 相似文献
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针对采用水玻璃、树脂等作为粘结剂进行铸件表面合金化时,合金层中容易产生气孔、夹渣缺陷的问题,研究了一种铸件表面合金化新工艺,即加入一种YB成型剂将合金粉末压制成块的方法进行表面合金化,在铸钢ZG65Mn本体表面得到高含Cr、W等元素的合金化层。结果表明,通过消失模铸造工艺,使用YB成型剂较好地消除了水玻璃等粘结剂造成的气孔、夹渣,合金化层和本体之间实现了冶金结合;合金化层具有较好的耐磨性和耐热性能,加入WC后耐磨性可达本体材料的4.82倍,抗氧化性能提高50%左右,且合金化粉末压块放置操作简便、可靠。 相似文献
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观察了铝合金激光深熔焊气孔的分布特征和形貌特征,深入分析了气孔的形成机理,研究了双光点能量分布的激光对铝合金激光深熔焊气孔的控制效果.结果表明,铝合金激光深熔焊焊缝中存在分布特征和形貌特征不同的两类气孔,即冶金类气孔和工艺类气孔.冶金类气孔的形成与氢在熔池中的析出、聚集与合并有关,而工艺类气孔产生的根本原因是焊接过程中匙孔的瞬间失稳.采用双光点能量分布的激光焊接铝合金可以扩大匙孔张口和根部直径,改善匙孔壁的波动状态,增强匙孔的稳定性,从而减少工艺类气孔的产生,但对冶金类气孔没有明显影响. 相似文献
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采用自主研制的超低碳氮强化药芯焊丝,利用明弧摆动堆焊技术,选择合适的堆焊工艺参数,在42CrMo板表面堆焊形成马氏体不锈钢堆焊层。通过超声波探伤仪、金相显微镜、EDS、显微硬度计分析测试堆焊层的组织、成分及性能。结果表明,堆焊层无裂纹、气孔等缺陷,与母材达到了冶金结合;堆焊层组织为单一的马氏体,其成分与所设计的药芯一致;堆焊层的硬度从底部到表层呈梯度变化,其平均硬度是基体的2.5倍,弥补了传统堆焊材料整体韧性不足的缺陷;氮化物均匀弥散分布在堆焊层表面。 相似文献
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在Ti6Al4V表面采用火焰喷焊技术制备硬质Ni基WC涂层,利用扫描电镜、显微硬度计、成分分析仪、X射线衍射仪进行组织形貌、显微硬度HV、EDS成分及相组成分析。分析结果表明:喷焊涂层由强化层、过渡层组成,涂层与基体结合紧密,与基体之间无分层、开裂等现象,涂层总厚度达到2400μm,涂层的表面硬度为11070MPa。涂层主要元素呈梯度变化,涂层硬度也呈相应的梯度变化。强化层中W原子配比大于C的原子配比,分子组合为WxC,WxC弥散分布于Ni基材料中,形成典型的韧Ni基体+硬质WxC的组织;WxC的出现是由于少量WC热分解为W2C;微量的氧化物存在于喷焊层表面,未在强化层整层中出现,其是喷焊层在放置冷却过程中出现的;强化层与过渡层之间无气孔等缺陷,两者有良好过渡。过渡层为Ni基材料与基体的互熔,形成良好的冶金层,过渡层与基体为冶金结合。 相似文献
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通过对有关文献的评述,讨论了连铸板坯皮下气泡的形成原因和分布特点,说明连铸过程中组合式结晶器角缝中上升气流吹入钢水可造成连铸坯皮下气泡。降低钢水过热度、降低拉速以促使结晶器内钢水尽快形成稳定坯壳,从而可以抵抗气流吹入,减轻皮下气泡的形成。由于在组合式结晶器内连铸坯皮下气泡的产生是难以避免的,所以棒材生产线的方坯连铸机不宜采用组合式结晶器,采用管式结晶器是当前的发展趋势。 相似文献
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A laser lap welding process for zinc-coated steel has a well-known unsolved problem-porosity formation. The boiling temperature of coated zinc is lower than the melting temperature of the base metal, which is steel. In the autogenous laser welding, the zinc vapor generates from the lapped surfaces expels the molten pool and the expulsion causes numerous weld defects, such as spatters and blow holes on the weld surface and porosity inside the welds. The laser-arc hybrid welding was suggested as an alternative method for the laser lap welding because the arc can preheat or post-heat the weldment according to the arrangement of the laser beam and the arc. CO2 laser-micro plasma hybrid welding was applied to the lap welding of zinc-coated steel with zero-gap. The relationships among the weld quality and process parameters of the laser-arc arrangement, and the laser-arc interspacing distance and arc current were investigated using a full-factorial experimental design. The effect of laser-arc arrangement is dominant because the leading plasma arc partially melts the upper steel sheets and vaporizes or oxidizes the coated zinc on the lapped surfaces. Compared with the result from the laser-TIG hybrid welding, the heat input from arc can be reduced by 40%. 相似文献
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Dr. C. R. Chakravorty Dr. M. Chakraborty 《International Journal of Cast Metals Research》2013,26(1):37-42
AbstractMetal-mould reactions in casting Al-Li alloys in sodium-silicate-bonded sand moulds have been studied by the modified Gertsman technique. Molten Al-2.7% Li alloy was poured into a bottom-gated vertical cylindrical mould cavity (150 mm x 50 mm dia) made from no-bake organic-binder-based sands. At the bottom of the mould cavity, a standard AFS three-ram sodium-silicate-bonded sand sample (the test sample) was placed vertically to provide the necessary interface for investigation. After cooling, the reaction products formed at the interface and samples from the bottom portion of the castings were collected for investigation. These were analysed to find Li loss from the casting as a result of metal-mould reactions. The casting was vertically sectioned and visually observed for appearance of blow holes, if any, while the sub-surface was studied for microhardness variation. The as-cast surface and the reaction products were also studied by SEM and X-ray diffraction analysis.The study reveals that the Li in the molten alloy enters into vigorous chemical reaction with the sodium silicate resulting in the release of metallic sodium and formation of reaction products containing αLithium aluminium meta silicate. Li is thus lost from near the surface of the casting. Probably, the sodium released causes the gas blow holes in the sub-surface of castings due to its high vapour pressure at the working temperature. 相似文献
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熔模铸钢件气孔的产生与防止 总被引:2,自引:0,他引:2
将熔模铸钢件的气孔分为析出性、侵入性、卷入性3种类型,其中析出性气孔又分为过溶析出性和反应析出性两类,详细论述了熔模铸钢件这几类气孔的形态、产生原因及防止措施。 相似文献
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Regarding intersecting holes, the edges of cut are often difficult to access, as they are located inside the components. Hence
it requires a lot of time and money to deburr them. In addition, burrs which come off in the later operation can lead to resultant
damages. Examinations of intersecting holes showed that the effective exit surface angle, the angle between drill wall and
exit surface, is crucial for burr formation. Based on the burr calculation for exit surfaces perpendicular to the drill axis,
a method of calculation was developed out of the experimental results. By means of this calculation method the burr value
g can be predicted for the short hole drilling of intersecting holes. 相似文献