【摘要】：鎂合金的焊接、腐蝕及防護問題與其應用密切相關,隨著焊接技術的快速發(fā)展,已實現(xiàn)了鎂合金構件的高性能連接。而針對鎂合金焊接接頭的腐蝕行為、防護機制及其與接頭顯微結構相關性的研究開展較少。因此,系統(tǒng)開展鎂合金攪拌摩擦焊(FSW)接頭的腐蝕行為與防護技術的研究,揭示接頭的腐蝕機制、為接頭的防護以及提高其服役壽命,具有重要的理論意義和實際價值。本文以AZ31鎂合金攪拌摩擦焊接頭為研究對象,分析了攪拌摩擦焊接參數(shù)對接頭顯微組織及力學性能的影響,針對鎂合金耐蝕性差的特點,系統(tǒng)的研究了接頭在NaCl溶液中的腐蝕行為,并采用冷噴涂純鋁的方法對其進行防護,獲得以下主要結論。FSW焊接工藝的改變,會引起焊接熱輸入量的變化,熱輸入量過大或過小都會造成接頭成形差、力學性能低;在焊接速度120mm/min,攪拌頭轉速轉速1200r/min時,焊縫成形良好,抗拉強度最高,達221.7MP,約為母材強度的83%。在不同的熱處理溫度及保溫時間下,焊接接頭各區(qū)域組織會產(chǎn)生不同的變化,組織形態(tài)的改變會引起硬度產(chǎn)生相應的變化。在熱處理溫度T=250℃保溫時間t=2h時,焊接接頭各區(qū)域組織趨于均勻化,平均顯微硬度不低于78Hv達到最高。AZ31鎂合金FSW焊縫的腐蝕電位和母材相近,而母材的腐蝕電流密度為0.00045A/cm2,焊縫為0.00163A/cm2,相差近一個數(shù)量級。由于焊接接頭的焊縫區(qū)受到晶粒尺寸及β相析出的影響,導致焊縫耐蝕性能最差,腐蝕最先從該區(qū)域產(chǎn)生。針對AZ31鎂合金FSW焊縫的耐蝕性不如母材的耐蝕性好的缺點,通過冷噴涂工藝優(yōu)化,在給粉機轉速R=0.4r/min進給速度S=600mm/min時,獲得了與機體結合緊密、孔隙率低的涂層。純鋁涂層自腐蝕電位高、腐蝕電流降低,所能明顯改善焊接接頭的耐腐蝕性能。由此可見,本文通過研究焊接接頭的腐蝕機制,掌握焊接接頭關鍵部位的腐蝕規(guī)律,采用了合理的防護措施,實現(xiàn)了對AZ31鎂合金攪拌摩擦焊接接頭的長效防護。
[Abstract]:The welding, corrosion and protection of magnesium alloy are closely related to its application. With the rapid development of welding technology, the high performance connection of magnesium alloy components has been realized. However, few researches have been carried out on the corrosion behavior of magnesium alloy welded joints, the protective mechanism and their correlation with the microstructure of the joints. Therefore, it is of great theoretical significance and practical value to systematically study the corrosion behavior and protection technology of magnesium alloy friction stir welding (FSW) joints, to reveal the corrosion mechanism of the joints, to protect the joints and to improve their service life. In this paper, the effect of friction stir welding parameters on microstructure and mechanical properties of AZ31 magnesium alloy friction stir welding joint is analyzed. The corrosion behavior of joints in NaCl solution was systematically studied, and the cold sprayed pure aluminum was used to protect the joints. The following main conclusions were obtained: the change of welding process of FSW would cause the change of welding heat input. When the welding speed is 120mm / min and the speed of stirring head is 1200r/min, the weld is formed well and the tensile strength is the highest (221.7 MPP), which is about 833% of the base metal strength. Under different heat treatment temperature and holding time, the microstructure of welded joint will change in different regions, and the change of microstructure will lead to the corresponding change of hardness. When the heat treatment temperature is 250 鈩，

本文編號：2139097