下軸肩冷卻對6061-T6鋁合金雙軸肩攪拌摩擦焊接頭性能的影響
發(fā)布時(shí)間：2018-09-08 15:50
【摘要】：雙軸肩攪拌摩擦焊(BTFSW)是由常規(guī)攪拌摩擦焊(FSW)進(jìn)一步發(fā)展而來,利用BTFSW有兩個(gè)軸肩的特點(diǎn),將兩個(gè)軸肩所受的作用力相互抵消,有效的減小了主軸負(fù)載,突破了焊機(jī)對剛性的限制、并能改善焊縫的根部缺陷。但在BTFSW焊接過程中,上軸肩與焊機(jī)夾持部分接觸,散熱條件好,下軸肩體積小,散熱條件差,導(dǎo)致接頭上下表面存在溫度差,從而影響焊縫成形質(zhì)量。如何在保證焊接質(zhì)量的前提下,降低雙軸肩攪拌頭下軸肩的溫度,平衡焊件上下表面熱量,減小上下表面溫度差成為BTFSW的急需解決的難題。本課題將針對原雙軸肩攪拌頭的缺點(diǎn),設(shè)計(jì)新型的雙軸肩攪拌頭以及配套的冷卻裝置。將冷卻裝置安裝在雙軸肩攪拌頭的下軸肩底部,使用螺紋配合與攪拌針連接。焊接時(shí),冷卻裝置隨著雙軸肩攪拌頭一同旋轉(zhuǎn),帶動冷卻液流過冷卻裝置,帶走大量焊接熱,最終實(shí)現(xiàn)循環(huán)冷卻。冷卻裝置主要對攪拌頭下軸肩進(jìn)行冷卻,在帶走多余焊接熱量的同時(shí),平衡接頭的上下表面溫度。通過研究下軸肩冷卻對6061鋁合金雙軸肩攪拌摩擦焊接頭性能影響,能更好的分析冷卻條件對于焊接熱循環(huán)的調(diào)節(jié)作用,同時(shí)在研究相變與焊接熱循環(huán)以及與接頭組織性能的關(guān)系基礎(chǔ)上,可以有效的對焊接參數(shù)進(jìn)行優(yōu)化,提高接頭性能,為6061-T6鋁合金的雙軸肩攪拌摩擦焊接奠定理論和工藝基礎(chǔ)。試驗(yàn)結(jié)果表明:在旋轉(zhuǎn)速度為810 r/min,焊接速度為160 mm/min條件下,對下軸肩冷卻可以使工件焊接時(shí)得到焊縫表面美觀,且無明顯孔洞隧道等缺陷。通過對有冷卻裝置的BTFSW進(jìn)行溫度場研究,發(fā)現(xiàn)使用冷卻裝置可以降低接頭區(qū)域整體的溫度,其中對接頭的下表面冷卻作用最為顯著,同時(shí)縮小了被焊工件上下表面的溫度差,保證焊縫的上下表面受熱均勻。使用冷卻裝置,還可以使工件在各溫度區(qū)間的持續(xù)時(shí)間減少,高溫持續(xù)時(shí)間的縮短抑制了晶粒生長,細(xì)化了晶粒組織,提高了接頭強(qiáng)度;使用冷卻裝置后,接頭區(qū)域的整體范圍變窄,接頭寬度減小了約4mm,焊核區(qū)晶粒粒度變小,排列更為均勻,硬度普遍提高,硬度最小值從55HV提高到60HV;熱機(jī)影響區(qū)范圍縮小,強(qiáng)化相析出量增多,同時(shí)晶粒長大收受抑制,平均硬度提高,強(qiáng)度增加;熱影響區(qū)范圍減小,前進(jìn)側(cè)硬度有所降低,這是由于前進(jìn)側(cè)溫度過低所致。
[Abstract]:(BTFSW) is further developed from conventional friction stir welding (FSW). By using the characteristics of BTFSW with two shafts, the interaction between the two shafts is counteracted, and the spindle load is effectively reduced. It breaks through the rigidity limitation of welding machine and can improve the root defect of welding seam. However, in the process of BTFSW welding, the upper shaft shoulder is in contact with the welding machine partly, the heat dissipation condition is good, the lower shaft shoulder volume is small, and the heat dissipation condition is poor, which leads to the temperature difference between the upper and lower surfaces of the joint, thus affecting the weld forming quality. On the premise of ensuring welding quality, how to reduce the temperature of the lower shaft shoulder of the double shaft shoulder stirring head, balance the upper and lower surface heat of the welding piece, and reduce the temperature difference between the upper and lower surface are the urgent problems for BTFSW to solve. In view of the shortcomings of the original double-shaft shoulder mixing head, a new type of double-shaft shoulder mixing head and its supporting cooling device will be designed in this paper. Install the cooling device at the bottom of the lower shaft shoulder of the double shaft shoulder mixing head, and connect with the stirring needle with the thread fit. During welding, the cooling device rotates with the double shaft shoulder mixing head together, drives the coolant to flow through the cooling device, takes away a large amount of welding heat, and finally realizes the circulation cooling. The cooling device is mainly used to cool the lower shaft shoulder of the mixing head and balance the upper and lower surface temperature of the joint while taking away the excess welding heat. By studying the effect of lower shaft shoulder cooling on the performance of 6061 aluminum alloy double shaft shoulder friction stir welding joint, the effect of cooling condition on welding thermal cycle can be better analyzed. At the same time, on the basis of studying the relationship between phase transformation and welding thermal cycle, as well as the microstructure and properties of the joint, the welding parameters can be effectively optimized, and the properties of the joint can be improved, thus laying a theoretical and technological foundation for the 6061-T6 aluminum alloy double-axle shoulder friction stir welding. The experimental results show that under the condition of rotating speed of 810 r / min and welding speed of 160 mm/min, cooling of the lower axle shoulder can make the weld surface beautiful when welding, and there are no obvious defects such as hole tunnel and so on. Through the research on the temperature field of BTFSW with cooling device, it is found that using the cooling device can reduce the whole temperature of the joint area, and the cooling effect on the lower surface of the joint is the most significant, and the temperature difference between the upper and lower surfaces of the welded workpiece is reduced at the same time. Ensure that the upper and lower surfaces of the weld are evenly heated. The use of the cooling device can also reduce the duration of the workpiece in each temperature range, the shortening of the high temperature duration inhibits the grain growth, refines the grain structure, and improves the strength of the joint. The overall area of the joint becomes narrower, the width of the joint decreases by about 4 mm, the grain size of the nugget becomes smaller, the arrangement is more uniform, the hardness is generally increased, and the minimum hardness is increased from 55HV to 60 HV.The area affected by the heat engine decreases, and the amount of enhanced phase precipitation increases. At the same time, the average hardness increases and the strength increases with the inhibition of grain growth, while the range of the heat affected zone decreases and the hardness of the forward side decreases, which is due to the low temperature of the front side.
【學(xué)位授予單位】：江蘇科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG457.14
本文編號：2230976
[Abstract]:(BTFSW) is further developed from conventional friction stir welding (FSW). By using the characteristics of BTFSW with two shafts, the interaction between the two shafts is counteracted, and the spindle load is effectively reduced. It breaks through the rigidity limitation of welding machine and can improve the root defect of welding seam. However, in the process of BTFSW welding, the upper shaft shoulder is in contact with the welding machine partly, the heat dissipation condition is good, the lower shaft shoulder volume is small, and the heat dissipation condition is poor, which leads to the temperature difference between the upper and lower surfaces of the joint, thus affecting the weld forming quality. On the premise of ensuring welding quality, how to reduce the temperature of the lower shaft shoulder of the double shaft shoulder stirring head, balance the upper and lower surface heat of the welding piece, and reduce the temperature difference between the upper and lower surface are the urgent problems for BTFSW to solve. In view of the shortcomings of the original double-shaft shoulder mixing head, a new type of double-shaft shoulder mixing head and its supporting cooling device will be designed in this paper. Install the cooling device at the bottom of the lower shaft shoulder of the double shaft shoulder mixing head, and connect with the stirring needle with the thread fit. During welding, the cooling device rotates with the double shaft shoulder mixing head together, drives the coolant to flow through the cooling device, takes away a large amount of welding heat, and finally realizes the circulation cooling. The cooling device is mainly used to cool the lower shaft shoulder of the mixing head and balance the upper and lower surface temperature of the joint while taking away the excess welding heat. By studying the effect of lower shaft shoulder cooling on the performance of 6061 aluminum alloy double shaft shoulder friction stir welding joint, the effect of cooling condition on welding thermal cycle can be better analyzed. At the same time, on the basis of studying the relationship between phase transformation and welding thermal cycle, as well as the microstructure and properties of the joint, the welding parameters can be effectively optimized, and the properties of the joint can be improved, thus laying a theoretical and technological foundation for the 6061-T6 aluminum alloy double-axle shoulder friction stir welding. The experimental results show that under the condition of rotating speed of 810 r / min and welding speed of 160 mm/min, cooling of the lower axle shoulder can make the weld surface beautiful when welding, and there are no obvious defects such as hole tunnel and so on. Through the research on the temperature field of BTFSW with cooling device, it is found that using the cooling device can reduce the whole temperature of the joint area, and the cooling effect on the lower surface of the joint is the most significant, and the temperature difference between the upper and lower surfaces of the welded workpiece is reduced at the same time. Ensure that the upper and lower surfaces of the weld are evenly heated. The use of the cooling device can also reduce the duration of the workpiece in each temperature range, the shortening of the high temperature duration inhibits the grain growth, refines the grain structure, and improves the strength of the joint. The overall area of the joint becomes narrower, the width of the joint decreases by about 4 mm, the grain size of the nugget becomes smaller, the arrangement is more uniform, the hardness is generally increased, and the minimum hardness is increased from 55HV to 60 HV.The area affected by the heat engine decreases, and the amount of enhanced phase precipitation increases. At the same time, the average hardness increases and the strength increases with the inhibition of grain growth, while the range of the heat affected zone decreases and the hardness of the forward side decreases, which is due to the low temperature of the front side.
【學(xué)位授予單位】：江蘇科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG457.14
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