6061鋁合金薄板無針攪拌摩擦焊工藝研究與微觀組織分析
發(fā)布時(shí)間：2018-10-07 18:32
【摘要】：6000系鋁合金作為性能優(yōu)異且使用廣泛的輕質(zhì)合金材料,擁有成為汽車輕量化制造原材料的巨大潛力。然而6000系鋁合金使用傳統(tǒng)焊接方法難以獲得優(yōu)質(zhì)的焊縫,鋁合金薄板更是如此。因此對(duì)于6000系鋁合金薄板連接技術(shù)的研究十分必要,近年來出現(xiàn)的一種名為無針攪拌摩擦焊的新型焊接技術(shù)能獲得優(yōu)質(zhì)穩(wěn)定的薄板鋁合金焊縫,但目前缺少對(duì)于6000系鋁合金薄板無針攪拌摩擦焊工藝的系統(tǒng)性研究。本研究選擇1mm厚6061-T6鋁合金薄板作為焊接材料,使用無針FSW技術(shù),針對(duì)影響接頭性能的主要焊接參數(shù)包括:主軸轉(zhuǎn)速、焊接速度、下壓量設(shè)計(jì)實(shí)驗(yàn)方案,獲得對(duì)焊與搭焊兩種形式的焊縫。測試焊縫力學(xué)拉伸性能與橫截面顯微硬度;采用金相顯微鏡觀察焊縫區(qū)缺陷;電子背散射衍射技術(shù)(EBSD)觀察焊縫區(qū)域材料晶粒尺寸與形狀;掃描電鏡(SEM)觀察分析拉伸斷口形貌。主要結(jié)論如下:6061鋁合金薄板無針FSW對(duì)焊實(shí)驗(yàn)所獲得的焊縫成形較為美觀。焊縫抗拉強(qiáng)度隨焊接速度的增加呈現(xiàn)先升后降的趨勢,峰值為198MPa,達(dá)到母材的73.4%。延伸率隨主軸轉(zhuǎn)速的升高而變大,最大值為20%。下壓量對(duì)焊縫抗拉強(qiáng)度有一定影響,本研究中最優(yōu)下壓量為0.1mm。自然時(shí)效能夠有效提升焊縫的力學(xué)拉伸性能。焊縫橫截面顯微硬度分布為“W”形或“一”字形,抗拉強(qiáng)度高的焊縫顯微硬度最小值更大。拉伸試樣斷裂位置基本位于焊縫中心處。光學(xué)顯微觀察結(jié)果顯示焊縫背部沒有未焊透缺陷。本研究最佳對(duì)焊工藝方案為:主軸轉(zhuǎn)速1500rpm,焊接速度300mm/min,下壓量0.1mm,焊后自然時(shí)效一周以上。6061鋁合金薄板無針FSW搭焊焊縫外觀無明顯缺陷,焊縫力學(xué)拉伸性能隨焊接速度升高為先升后降的趨勢,最大值為199.5MPa,達(dá)到母材的73.9%。焊縫橫截面顯微硬度測試結(jié)果表明,無針FSW搭焊接頭上、下板顯微硬度為“W”或“一”字形分布;上板硬度下降區(qū)域大于下板;力學(xué)拉伸性能好的無針FSW搭焊接頭顯微硬度最小值更大。拉伸試樣斷裂于上板后退側(cè)熱影響區(qū)。光學(xué)顯微觀察結(jié)果顯示,力學(xué)拉伸性能好的焊縫上、下板之間的融合區(qū)域更寬,高轉(zhuǎn)速的焊縫前進(jìn)側(cè)容易出現(xiàn)Hook缺陷。最優(yōu)工藝參數(shù)為:主軸轉(zhuǎn)速1500rpm,焊接速度300mm/min,下壓量0.1mm。采用EBSD觀察性能最好的無針FSW對(duì)焊與搭焊焊縫,發(fā)現(xiàn)對(duì)焊與搭焊焊縫上板焊縫中心位置的組織是經(jīng)歷劇烈塑性變形后的細(xì)小等軸晶,熱機(jī)影響區(qū)同時(shí)受塑性變形與熱循環(huán)作用,晶粒大小不均勻,熱影響區(qū)只受熱循環(huán)作用,晶粒最大;搭焊焊縫下板都是受熱長大的粗大晶粒。從拉伸斷口的SEM結(jié)果來看,高延伸率對(duì)焊焊縫為韌性拉伸斷裂,搭焊焊縫都為脆性斷裂。
[Abstract]:As a light alloy material with excellent properties and wide use, 6000 series aluminum alloy has great potential as raw material for automobile lightweight manufacturing. However, it is difficult to obtain high quality welding seam for 6000 series aluminum alloy by traditional welding method, especially for aluminum alloy sheet. Therefore, it is necessary to study the joining technology of 6000 series aluminum alloy sheet. In recent years, a new type of welding technology called needle-free friction stir welding can obtain high quality and stable thin aluminum alloy weld. However, there is a lack of systematic research on the non-needle friction stir welding process for 6000 series aluminum alloy sheet. In this study, 1mm thick 6061-T6 aluminum alloy sheet is selected as welding material, and the needle-free FSW technology is used. The main welding parameters that affect the performance of joint include: spindle speed, welding speed, down pressure design experimental scheme. Two types of weld seam, butt welding and lap welding, are obtained. The mechanical tensile properties and cross section microhardness of the weld were tested; the defects in the weld zone were observed by metallographic microscope; the grain size and shape of the weld material were observed by electron backscatter diffraction (EBSD); and the tensile fracture morphology was observed and analyzed by SEM (SEM). The main conclusions are as follows: 1. The weld shape obtained by needle-free FSW butt welding experiment is more beautiful. The tensile strength of the weld increases first and then decreases with the increase of welding speed, and the peak value is 198 MPA, reaching 73.4% of the base metal. The elongation increases with the increase of spindle speed, and the maximum value is 20. The drop pressure has a certain effect on the tensile strength of the weld, and the optimum drop pressure is 0.1 mm. in this study. Natural aging can effectively improve the mechanical tensile properties of the weld. The microhardness distribution of cross section of weld is "W" or "one", and the minimum value of micro-hardness of weld with high tensile strength is larger. The fracture position of tensile specimen is basically located at the center of weld. The results of optical microscopic observation showed that there was no penetration defect in the back of the weld. The optimum butt welding process scheme is as follows: spindle speed 1500 rpm, welding speed 300 mm / min, pressure 0.1 mm, welding appearance no obvious defect in the welding seam of natural aging more than one week after welding, without needle FSW welding of aluminum alloy sheet, and the welding speed is 300mm / min, and the welding speed is 0.1 mm / min. With the increase of welding speed, the mechanical tensile properties of the weld increased first and then decreased, and the maximum value was 199.5MPa, which reached 73.9 of the base metal. The results of microhardness test of weld cross section show that the microhardness of the lower plate is "W" or "one" distribution on the top of the welded joint without needle FSW, and the decreasing area of the hardness of the upper plate is larger than that of the lower plate. The minimum microhardness of needle-less FSW lap welded joints with good tensile properties is higher. The tensile specimen is fractured in the heat affected zone of the receding side of the upper plate. The results of optical microscopic observation show that the fusion area between the lower plates is wider in the weld with good mechanical tensile properties, and the Hook defects are easy to appear in the forward side of the weld at high speed. The optimum technological parameters are as follows: spindle rotation speed 1500 rpm, welding speed 300 mm / min, down pressure 0.1mm. EBSD was used to observe the best non-needle FSW butt welding and lap welding weld. It was found that the microstructure of weld center of butt welding and lap weld was small equiaxed crystal after severe plastic deformation, and the influence zone of heat engine was affected by plastic deformation and thermal cycling simultaneously. The grain size is not uniform, the heat affected zone is only affected by heat cycling, the grain size is the largest, and the bottom plate of lap welding weld is the coarse grain grown by heating. According to the SEM results of tensile fracture, the high elongation butt weld is ductile tensile fracture, while the lap weld is brittle fracture.
【學(xué)位授予單位】：重慶交通大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG453.9;TG146.21
本文編號(hào)：2255240
[Abstract]:As a light alloy material with excellent properties and wide use, 6000 series aluminum alloy has great potential as raw material for automobile lightweight manufacturing. However, it is difficult to obtain high quality welding seam for 6000 series aluminum alloy by traditional welding method, especially for aluminum alloy sheet. Therefore, it is necessary to study the joining technology of 6000 series aluminum alloy sheet. In recent years, a new type of welding technology called needle-free friction stir welding can obtain high quality and stable thin aluminum alloy weld. However, there is a lack of systematic research on the non-needle friction stir welding process for 6000 series aluminum alloy sheet. In this study, 1mm thick 6061-T6 aluminum alloy sheet is selected as welding material, and the needle-free FSW technology is used. The main welding parameters that affect the performance of joint include: spindle speed, welding speed, down pressure design experimental scheme. Two types of weld seam, butt welding and lap welding, are obtained. The mechanical tensile properties and cross section microhardness of the weld were tested; the defects in the weld zone were observed by metallographic microscope; the grain size and shape of the weld material were observed by electron backscatter diffraction (EBSD); and the tensile fracture morphology was observed and analyzed by SEM (SEM). The main conclusions are as follows: 1. The weld shape obtained by needle-free FSW butt welding experiment is more beautiful. The tensile strength of the weld increases first and then decreases with the increase of welding speed, and the peak value is 198 MPA, reaching 73.4% of the base metal. The elongation increases with the increase of spindle speed, and the maximum value is 20. The drop pressure has a certain effect on the tensile strength of the weld, and the optimum drop pressure is 0.1 mm. in this study. Natural aging can effectively improve the mechanical tensile properties of the weld. The microhardness distribution of cross section of weld is "W" or "one", and the minimum value of micro-hardness of weld with high tensile strength is larger. The fracture position of tensile specimen is basically located at the center of weld. The results of optical microscopic observation showed that there was no penetration defect in the back of the weld. The optimum butt welding process scheme is as follows: spindle speed 1500 rpm, welding speed 300 mm / min, pressure 0.1 mm, welding appearance no obvious defect in the welding seam of natural aging more than one week after welding, without needle FSW welding of aluminum alloy sheet, and the welding speed is 300mm / min, and the welding speed is 0.1 mm / min. With the increase of welding speed, the mechanical tensile properties of the weld increased first and then decreased, and the maximum value was 199.5MPa, which reached 73.9 of the base metal. The results of microhardness test of weld cross section show that the microhardness of the lower plate is "W" or "one" distribution on the top of the welded joint without needle FSW, and the decreasing area of the hardness of the upper plate is larger than that of the lower plate. The minimum microhardness of needle-less FSW lap welded joints with good tensile properties is higher. The tensile specimen is fractured in the heat affected zone of the receding side of the upper plate. The results of optical microscopic observation show that the fusion area between the lower plates is wider in the weld with good mechanical tensile properties, and the Hook defects are easy to appear in the forward side of the weld at high speed. The optimum technological parameters are as follows: spindle rotation speed 1500 rpm, welding speed 300 mm / min, down pressure 0.1mm. EBSD was used to observe the best non-needle FSW butt welding and lap welding weld. It was found that the microstructure of weld center of butt welding and lap weld was small equiaxed crystal after severe plastic deformation, and the influence zone of heat engine was affected by plastic deformation and thermal cycling simultaneously. The grain size is not uniform, the heat affected zone is only affected by heat cycling, the grain size is the largest, and the bottom plate of lap welding weld is the coarse grain grown by heating. According to the SEM results of tensile fracture, the high elongation butt weld is ductile tensile fracture, while the lap weld is brittle fracture.
【學(xué)位授予單位】：重慶交通大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG453.9;TG146.21
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