本文選題：鎂合金 + 活性焊接��； 參考：《沈陽工業(yè)大學》2017年碩士論文

【摘要】：在現(xiàn)有的工程用金屬中,鎂合金的密度最小并且具有強度高、剛性好等一系列優(yōu)點,在汽車、航空航天和運動器材等領(lǐng)域有著廣泛的應用空間。但是鎂合金由于自身的物理化學特性,導致其焊接時易產(chǎn)生熱裂紋、氣孔、夾雜等缺陷,不容易獲得高質(zhì)量的焊接接頭。因此,提高鎂合金焊接性,獲得優(yōu)質(zhì)的焊接接頭是非常必要的。磁控焊接和活性焊接同傳統(tǒng)焊接相比具有成本低、效率高、質(zhì)量好等優(yōu)點,因此進行鎂合金活性焊接并且施加縱向磁場對改善鎂合金的焊接方法有著重要的實際意義。實驗采用A-TIG焊焊接AZ91鎂合金試板,焊接過程中外加縱向交流變頻磁場,并采用正交實驗對工藝參數(shù)進行優(yōu)化。焊接時采用高速攝像觀測電弧形態(tài)的變化,焊后,對不同參數(shù)下焊接接頭的成形狀態(tài)、接頭力學性能和顯微組織進行測試,研究其中的規(guī)律和機理,主要研究結(jié)果為:(1)正交實驗結(jié)果表明,在縱向磁場和氯化物活性劑聯(lián)合作用下,四個因素對焊縫成形系數(shù)的影響由大到小分別為:磁場頻率磁場電流焊接電流涂覆量。當磁場電流為3.5A、磁場頻率為30Hz、焊接電流為85A、涂覆量為1mg/cm2時,AZ91鎂合金焊縫的硬度達到最大值73.83HV,此時焊接接頭顯微組織由α-Mg基體和沿晶界彌散分布的β-Al12Mg17第二相組成,晶粒細化明顯,故力學性能得到提高。(2)根據(jù)正交實驗發(fā)現(xiàn)在縱向磁場和氧化物活性劑聯(lián)合作用下,四個因素對焊縫成形系數(shù)的影響由大到小分別為:涂覆量磁場頻率磁場電流焊接電流。最佳參數(shù)為磁場電流1.5A、磁場頻率30Hz、焊接電流80A、涂覆量3mg/cm2,焊縫硬度達到最大值76.3HV。此時焊縫組織細小,力學性能提高明顯。(3)基于高速攝影技術(shù)可以發(fā)現(xiàn),施加縱向磁場電弧會發(fā)生旋轉(zhuǎn)并且收縮明顯。磁場對焊接熔池起著電磁攪拌的作用,使焊接接頭組織細化。當涂覆氧化物活性劑進行焊接時,氧元素能夠使改變?nèi)鄢氐牧鲃臃绞绞购缚p的熔深增加。當涂覆氯化物活性劑進行焊接時,氯化物活性劑作用于電弧從而使試件熔深增加。
[Abstract]:Magnesium alloy has a series of advantages such as low density, high strength, good rigidity and so on, among the existing engineering metals, it has a wide range of applications in the fields of automobile, aerospace, sports equipment and so on. However, due to its physical and chemical characteristics, magnesium alloys are prone to heat cracks, pores, inclusions and other defects during welding, so it is not easy to obtain high quality welded joints. Therefore, it is necessary to improve the weldability of magnesium alloy and obtain high quality welded joints. Compared with conventional welding, magnetically controlled welding and active welding have the advantages of low cost, high efficiency and good quality. Therefore, it is of great practical significance to improve the welding method of magnesium alloy by applying longitudinal magnetic field and active welding. In the experiment, the AZ91 magnesium alloy test plate was welded by A-TIG welding, and the longitudinal AC variable frequency magnetic field was added in the welding process, and the process parameters were optimized by orthogonal experiment. After welding, the forming state, mechanical properties and microstructure of welded joints under different parameters were tested, and the rules and mechanisms were studied. The main results are as follows: (1) orthogonal experiment results show that the influence of four factors on the weld formation coefficient under the combined action of longitudinal magnetic field and chloride active agent is as follows: magnetic field frequency magnetic field current welding current coating amount. When the magnetic field current is 3.5A, the magnetic field frequency is 30Hz, the welding current is 85A, and the coating amount is 1mg/cm2, the hardness of the weld seam of AZ91 magnesium alloy reaches the maximum value of 73.83HV.The microstructure of the welded joint is composed of 偽 -Mg matrix and the second phase of 尾 -Al12Mg17 dispersed along the grain boundary, and the grain refinement is obvious. Therefore, the mechanical properties are improved. (2) according to the orthogonal experiment, it is found that the influence of four factors on the weld formation coefficient under the combined action of longitudinal magnetic field and oxide active agent is as follows: coating magnetic field frequency magnetic field current welding current. The optimum parameters are magnetic current 1.5 A, magnetic frequency 30 Hz, welding current 80 A, coating amount 3 mg / cm 2, and weld hardness reaching the maximum value of 76.3 HV. On the basis of high speed photography, it can be found that the longitudinal magnetic arc will rotate and shrink obviously. Magnetic field plays the role of electromagnetic stirring in weld pool, which makes the microstructure of welded joint fine. When the oxide active agent is applied in welding, oxygen can increase the weld penetration by changing the flow mode of the weld pool. When coated with chlorides for welding, chlorides act on the arc to increase the penetration of the specimens.
【學位授予單位】：沈陽工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG407

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