铸造镁合金A-TIG补焊工艺研究
发布时间：2019-03-13 18:54
【摘要】：镁合金因其具有优良特性,被广泛应用于航空航天、汽车、电子通讯等领域,通过镁合金零部件的使用可以有效地实现轻量化目标。由于变形镁合金生产成本比较高,目前工业应用的镁合金以铸造件为主,镁合金在铸造过程中极易出现各种类型的缺陷,如气孔、裂纹等,或者机械加工和运输过程中产生的缺陷而使铸件成为不合格品,不仅造成了材料的极大浪费而且影响产品的交付使用,所以对铸件缺陷的修补具有重要的经济效益和社会效益。镁合金铸件的补焊采用较多的是传统钨极惰性气体保护焊(TIG),但是因其低生产效率、低成品率,不能满足工程上铸件补焊要求。为了提高TIG焊焊缝熔深并且改善焊缝质量,人们提出活性化钨极氩弧焊(Activating Flux TIG,A-TIG)焊接方法,A-TIG焊焊接方法是焊前在母材表面涂敷一层活性剂,在相同焊接规范下,A-TIG焊具有增加焊缝熔深、大幅度地消减焊缝气孔等优势。因此,本文将A-TIG焊焊接方法应用于铸造镁合金补焊,提出一种新型A-TIG补焊方法,研究其与TIG补焊工艺的区别,以便提高补焊效率和成品率。模拟补焊铸造镁合金孔洞类缺陷试验,同焊接参数条件下(I=120A, V=5mm/s),TIG补焊铸造镁合金只可以愈合lmm深的孔洞,而A-TIG可以愈合3mm深的孔洞；同愈合程度条件下(孔深h=3mm、孔径口=3mm) TIG补焊铸造镁合金在焊接电流200A时可以获得同A-TIG补焊在焊接电流120A时相同的愈合效果,但是前者焊缝中出现明显的气孔缺陷；对变形镁合金进行模拟试验发现,A-TIG补焊能力优于TIG补焊能力,但补焊后的焊缝表面和纵截面没有发现焊接气孔缺陷,这说明变形镁合金和铸造镁合金母材的差异导致焊接气孔的产生；补焊后焊接接头的微观组织和显微硬度观察发现,利用A-TIG进行补焊不但可以实现较深孔洞的愈合,而且可以减少焊缝气孔缺陷,具有提高效率和减少缺陷的效果；为进一步减少补焊缺陷以及探究A-TIG补焊减少气孔缺陷的机理,进行A-TIG焊自动冷填丝工艺研究,采用后向送丝工艺进行铸造镁合金模拟孔洞类缺陷补焊试验,并且焊后没有发现气孔缺陷；A-TIG补焊能减少气孔缺陷主要Zr02活性剂能向焊缝中引入锆元素,提高焊缝固氢能力,A-TIG焊熔池内部流动性具有一致性,熔池侧壁自下向上运动,这种流动方式有助于气泡的排除；提出铸造镁合金补焊规范工艺及进行铸件补焊示范应用。
[Abstract]:Magnesium alloy is widely used in aerospace, automobile, electronic communication and other fields because of its excellent characteristics. The lightweight goal can be achieved effectively through the use of magnesium alloy parts. Because of the high production cost of wrought magnesium alloys, the main magnesium alloys used in industry at present are castings. Various kinds of defects, such as pores, cracks and so on, are easy to appear in the casting process of magnesium alloys. Or the defects in the process of machining and transportation cause the casting to become unqualified, which not only causes a great waste of materials but also affects the delivery and use of the products. Therefore, it has important economic and social benefits to repair the defects of castings. The traditional tungsten inert gas shielded arc welding (TIG),) is widely used in magnesium alloy castings, but because of its low production efficiency and low yield, it can not meet the requirements of engineering casting repair welding. In order to improve the penetration of TIG welding seam and improve the weld quality, the activated tungsten argon arc welding (Activating Flux TIG,A-TIG) welding method is proposed. The A-TIG welding method is to coat a layer of flux on the base metal surface before welding. Under the same welding criterion, A-TIG welding has the advantages of increasing weld penetration and reducing weld hole greatly. Therefore, in this paper, the A-TIG welding method is applied to the casting magnesium alloy repair welding, a new A-TIG repair welding method is proposed, and the difference between the A-TIG repair welding method and the TIG repair welding process is studied in order to improve the repair welding efficiency and the finished product rate. Under the condition of welding parameters (I, 120A, V=5mm/s), TIG), the casting magnesium alloy can only heal the deep holes of lmm, while A-TIG can heal the deep holes of 3mm under the condition of welding parameters (I) 120A, and the A-TIG can heal the deep holes of 3mm under the condition of the same welding parameters as the welding parameters. Under the condition of the same healing degree (3 mm hole depth, diameter = 3mm), the same healing effect can be obtained when the welding current is 200A in the casting magnesium alloy cast magnesium alloy as that in the A-TIG repair welding at the welding current of 120A, but there are obvious hole defects in the former weld. The simulation results of magnesium alloy show that A-TIG repair welding ability is superior to TIG repair welding ability, but the weld surface and longitudinal section after repair welding do not find the weld hole defect, but the welding hole defect is not found in the weld surface and longitudinal section after repair welding. This indicates that the difference between wrought magnesium alloy and cast magnesium alloy base metal results in the formation of welding pores. The microstructure and microhardness of welded joints after repair welding are observed. It is found that A-TIG can not only heal the deep holes, but also reduce the hole defects in the weld, and improve the efficiency and reduce the defects. In order to further reduce the defect of repair welding and explore the mechanism of reducing hole defect in A-TIG repair welding, the automatic cold wire filling technology of A-TIG welding was studied, and the casting magnesium alloy simulated hole defect repair welding test was carried out by the backward wire feeding process. No pore defects were found after welding. A-TIG repair welding can reduce the pore defects. The main Zr02 flux can introduce zirconium into the weld and improve the hydrogen fixation ability of the weld. The internal fluidity of the weld pool in A-TIG welding is consistent, and the side wall of the weld pool moves from bottom to bottom. This flow mode is helpful for the removal of bubbles. The specification and application of casting magnesium alloy repair welding are put forward.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG457.1
本文编号：2439678
[Abstract]:Magnesium alloy is widely used in aerospace, automobile, electronic communication and other fields because of its excellent characteristics. The lightweight goal can be achieved effectively through the use of magnesium alloy parts. Because of the high production cost of wrought magnesium alloys, the main magnesium alloys used in industry at present are castings. Various kinds of defects, such as pores, cracks and so on, are easy to appear in the casting process of magnesium alloys. Or the defects in the process of machining and transportation cause the casting to become unqualified, which not only causes a great waste of materials but also affects the delivery and use of the products. Therefore, it has important economic and social benefits to repair the defects of castings. The traditional tungsten inert gas shielded arc welding (TIG),) is widely used in magnesium alloy castings, but because of its low production efficiency and low yield, it can not meet the requirements of engineering casting repair welding. In order to improve the penetration of TIG welding seam and improve the weld quality, the activated tungsten argon arc welding (Activating Flux TIG,A-TIG) welding method is proposed. The A-TIG welding method is to coat a layer of flux on the base metal surface before welding. Under the same welding criterion, A-TIG welding has the advantages of increasing weld penetration and reducing weld hole greatly. Therefore, in this paper, the A-TIG welding method is applied to the casting magnesium alloy repair welding, a new A-TIG repair welding method is proposed, and the difference between the A-TIG repair welding method and the TIG repair welding process is studied in order to improve the repair welding efficiency and the finished product rate. Under the condition of welding parameters (I, 120A, V=5mm/s), TIG), the casting magnesium alloy can only heal the deep holes of lmm, while A-TIG can heal the deep holes of 3mm under the condition of welding parameters (I) 120A, and the A-TIG can heal the deep holes of 3mm under the condition of the same welding parameters as the welding parameters. Under the condition of the same healing degree (3 mm hole depth, diameter = 3mm), the same healing effect can be obtained when the welding current is 200A in the casting magnesium alloy cast magnesium alloy as that in the A-TIG repair welding at the welding current of 120A, but there are obvious hole defects in the former weld. The simulation results of magnesium alloy show that A-TIG repair welding ability is superior to TIG repair welding ability, but the weld surface and longitudinal section after repair welding do not find the weld hole defect, but the welding hole defect is not found in the weld surface and longitudinal section after repair welding. This indicates that the difference between wrought magnesium alloy and cast magnesium alloy base metal results in the formation of welding pores. The microstructure and microhardness of welded joints after repair welding are observed. It is found that A-TIG can not only heal the deep holes, but also reduce the hole defects in the weld, and improve the efficiency and reduce the defects. In order to further reduce the defect of repair welding and explore the mechanism of reducing hole defect in A-TIG repair welding, the automatic cold wire filling technology of A-TIG welding was studied, and the casting magnesium alloy simulated hole defect repair welding test was carried out by the backward wire feeding process. No pore defects were found after welding. A-TIG repair welding can reduce the pore defects. The main Zr02 flux can introduce zirconium into the weld and improve the hydrogen fixation ability of the weld. The internal fluidity of the weld pool in A-TIG welding is consistent, and the side wall of the weld pool moves from bottom to bottom. This flow mode is helpful for the removal of bubbles. The specification and application of casting magnesium alloy repair welding are put forward.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG457.1
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