局部軋制及熱處理對AZ系鎂合金焊接組織與性能的影響研究
發(fā)布時間：2018-12-14 07:53
【摘要】：鎂合金作為最輕的金屬結(jié)構(gòu)材料,具有比強(qiáng)度高,減震性、電磁屏蔽性強(qiáng),易切削加工、易回收等優(yōu)點(diǎn),在汽車、電子、航空航天和國防軍工領(lǐng)域具有較大的應(yīng)用潛力。然而,鎂合金的熔沸點(diǎn)、燃點(diǎn)都比較低,化學(xué)性質(zhì)活潑,焊接過程中容易出現(xiàn)氣孔、粗晶等問題,特別是焊接組織與母材組織之間的顯著差異,導(dǎo)致鎂合金焊接接頭的力學(xué)性能普遍較差,與母材相差甚遠(yuǎn),嚴(yán)重限制了鎂合金的發(fā)展與應(yīng)用。本文針對此問題,分別以雙面TIG焊的AZ31鎂合金和AZ80鎂合金為研究對象,對其進(jìn)行焊后加工,主要包括余高軋制和熱處理。通過實(shí)驗(yàn)結(jié)合模擬的方式,分析了焊縫余高軋制工藝的變形特點(diǎn),研究了不可熱處理強(qiáng)化的AZ31鎂合金和可熱處理強(qiáng)化的AZ80鎂合金,在焊后處理過程中的顯微組織、焊接氣孔以力學(xué)性能演化特點(diǎn),以及強(qiáng)化機(jī)理。主要研究結(jié)論如下:(1)模擬結(jié)果顯示,余高軋制過程中,焊接板材上的應(yīng)變分布并不均勻,分為咬入?yún)^(qū)、穩(wěn)定變形區(qū)和板材離輥區(qū),應(yīng)變分布與軋制壓下量緊密相關(guān)。余高軋制不僅使焊縫區(qū)發(fā)生變形,還會使焊縫周邊區(qū)域發(fā)生間接變形,對變形區(qū)實(shí)現(xiàn)形變強(qiáng)化,熱變形時還會激發(fā)動態(tài)再結(jié)晶,細(xì)化組織。(2)AZ31鎂合金焊接接頭的抗拉強(qiáng)度和延伸率,都隨著余高軋制壓下量的增加而顯著升高。當(dāng)壓下量達(dá)到一定值時,拉伸斷裂位置由焊縫轉(zhuǎn)移至母材,此時焊接接頭的拉伸性能幾乎與母材相同。焊接區(qū)的局部形變強(qiáng)化是AZ31鎂合金余高軋制過程中的最主要強(qiáng)化機(jī)制,室溫軋制即可大幅提升AZ31焊接接頭的力學(xué)性能,但是軋制壓下量超過20%后焊縫區(qū)容易開裂。變形溫度升高,可顯著提升焊接接頭的塑性,降低焊縫軋制開裂傾向,但同時會削弱形變強(qiáng)化效果,需要更大的變形量才能使焊縫區(qū)的強(qiáng)度高于母材,從而使斷裂位置轉(zhuǎn)移。(3)AZ80鎂合金經(jīng)過TIG焊后,焊縫區(qū)產(chǎn)生大量Mg17Al12相,會在后續(xù)的余高軋制過程中增強(qiáng)形變硬化效果,影響再結(jié)晶行為,而熱影響區(qū)的第二相溶解,失去了Mg17Al12相對晶界的釘扎作用,晶粒在后續(xù)固溶處理過程中很容易發(fā)生異常長大,導(dǎo)致該區(qū)域強(qiáng)度降低。合理的復(fù)合處理工藝,可在提高焊縫區(qū)強(qiáng)度的同時有效緩解熱影響區(qū)晶粒長大,充分改善鎂合金焊接接頭的組織性能。(4)鋁含量較高的AZ80鎂合金在焊接過程中更容易產(chǎn)生氣孔,余高軋制工藝可有效消除焊縫中的氣孔。隨著軋制壓下量的增加,氣孔逐漸閉合。軋制溫度偏低時,可能會在氣孔周圍產(chǎn)生裂紋,不利于焊接接頭的力學(xué)性能,軋制溫度升高可提高鎂合金塑性,避免裂紋的出現(xiàn)。(5)AZ80鎂合金的變形抗力較大,在低于300℃進(jìn)行余高軋制時焊縫很容易開裂,軋制過程難以進(jìn)行。在合理的軋制溫度范圍內(nèi),AZ80焊接接頭的綜合力學(xué)性能隨著軋制壓下量的增加而顯著升高,主要強(qiáng)化機(jī)制為形變強(qiáng)化、細(xì)晶強(qiáng)化以及焊縫中氣孔的閉合,幾種強(qiáng)化機(jī)制在350℃左右得到最好的配合。(6)AZ80焊接接頭在余高軋制后進(jìn)行時效的過程中,Mg17Al12相在孿晶界、孿晶內(nèi)外、變形區(qū)和未變形區(qū)的析出形貌、尺寸與分布都存在差異。采用余高軋制與熱處理相結(jié)合的焊后復(fù)合處理,可以控制各個區(qū)域的顯微組織,從而影響焊接接頭的力學(xué)性能。存在焊接氣孔的AZ80焊接接頭經(jīng)過焊后復(fù)合處理,屈服強(qiáng)度達(dá)到200MPa(母材的85%),抗拉強(qiáng)度314MPa(母材的88%),延伸率4.5%(母材的45%)。(7)無法得到焊縫余高或余高不足時,可對鎂合金焊接板材進(jìn)行無余高的整體熱軋,通過動態(tài)再結(jié)晶細(xì)化各區(qū)域顯微組織,縮小晶粒尺寸差異,提高焊接接頭強(qiáng)度。低溫短時間的去軋制應(yīng)力退火可使焊接接頭的塑性提升,得到更好的綜合力學(xué)性能。
[Abstract]:As the light metal structure material, the magnesium alloy has the advantages of high specific strength, shock absorption, strong electromagnetic shielding property, easy cutting and processing, easy recovery and the like, and has great application potential in the fields of automobile, electronics, aerospace and national defense and military industry. however, the melting point and the ignition point of the magnesium alloy are relatively low, the chemical property is active, and the problems of air holes, coarse crystals and the like in the welding process are easy to occur, in particular, the mechanical property of the magnesium alloy welding joint is generally poor, the mechanical property of the magnesium alloy welding joint is generally poor, and the welding joint of the magnesium alloy is far from the parent material, The development and application of the magnesium alloy are severely restricted. In this paper, the AZ31 magnesium alloy and the AZ80 magnesium alloy with double-side TIG welding are used as the research object, and the welding is carried out on the AZ31 magnesium alloy and the AZ80 magnesium alloy, which mainly comprises the following high rolling and heat treatment. In this paper, by means of experiment and simulation, the deformation characteristics of the weld residual high rolling process are analyzed, the non-heat-treated reinforced AZ31 magnesium alloy and the heat-treated reinforced AZ80 magnesium alloy are studied, and the microstructure and the welding hole in the post-welding process are characterized by mechanical property evolution, and the strengthening mechanism. The main research results are as follows: (1) The simulation results show that the strain distribution on the welded plate is not uniform during the high rolling process, and it is divided into the bite zone, the stable deformation zone and the plate-to-roll zone, and the strain distribution is closely related to the rolling reduction. The residual high rolling can not only deform the weld zone, but also cause indirect deformation of the peripheral area of the weld, and the deformation zone can be deformed and strengthened, and the dynamic recrystallization and the refining of the tissue can also be stimulated in the case of thermal deformation. (2) The tensile strength and the elongation of the AZ31 magnesium alloy welded joint increase with the increase of the rolling reduction. When the pressing amount reaches a certain value, the tensile fracture position is transferred to the mother material by the welding line, and the tensile property of the welded joint is almost the same as that of the mother material. The local deformation strengthening of the welding area is the main strengthening mechanism in the process of high-temperature rolling of the AZ31 magnesium alloy, and the mechanical property of the AZ31 welding joint can be greatly improved by rolling at room temperature, but the weld area is easy to crack after the rolling reduction exceeds 20%. the deformation temperature is increased, the plasticity of the welding joint can be obviously improved, the rolling and cracking tendency of the welding seam is reduced, the deformation strengthening effect is weakened at the same time, the strength of the weld zone is higher than that of the parent material, and the fracture position is transferred. and (3) after the AZ80 magnesium alloy is subjected to TIG welding, a large amount of Mg17Al12 phase is generated in the weld zone, the deformation hardening effect is enhanced during the subsequent high-high rolling process, the recrystallization behavior is influenced, and the second phase of the heat-affected zone is dissolved, and the pinning effect of the Mg17Al12 relative to the grain boundary is lost, The crystal grains tend to grow abnormally during the subsequent solid-dissolving process, resulting in a reduction in the strength of the region. The reasonable composite treatment process can effectively relieve the grain growth of the heat affected zone while improving the strength of the weld zone, and fully improve the tissue performance of the magnesium alloy welding joint. and (4) the AZ80 magnesium alloy with higher aluminum content can more easily generate air holes during the welding process, and the residual high rolling process can effectively eliminate the air holes in the welding seam. with the increase of the rolling reduction, the air holes are gradually closed. When the rolling temperature is low, cracks can be generated around the air holes, which is not beneficial to the mechanical property of the welding joint, and the rolling temperature is increased, so that the plasticity of the magnesium alloy can be improved, and the occurrence of cracks is avoided. and (5) the deformation resistance of the AZ80 magnesium alloy is large, and the welding seam is easy to crack when the residual high rolling is carried out at lower than 300 DEG C, and the rolling process is difficult to carry out. In the reasonable rolling temperature range, the comprehensive mechanical properties of the AZ80 welded joint are significantly increased with the increase of the rolling reduction, the main strengthening mechanism is the deformation strengthening, the fine grain strengthening and the closing of the air holes in the welding line, and several strengthening mechanisms are best matched at the temperature of about 350 DEG C. (6) The microstructure, size and distribution of the Mg17Al12 phase in the grain boundary, the inner and outer, the deformation zone and the undeformed zone of the AZ80 welded joint are different in the process of aging after the residual high rolling. The microstructure of each region can be controlled by the post-welding composite treatment combined with the combination of the residual high rolling and the heat treatment, so as to influence the mechanical property of the welded joint. The tensile strength of the AZ80 welded joint with the welding hole is 200MPa (85% of the parent material), the tensile strength is 314MPa (88% of the mother material), and the elongation rate is 4.5% (45% of the parent material). and (7) when the residual height or the residual height of the weld can not be obtained, the magnesium alloy welding plate can be subjected to a non-residual high-temperature hot rolling, and the microstructure of each region can be refined by dynamic recrystallization, so that the grain size difference can be reduced, and the strength of the welding joint can be improved. the low-temperature short-time rolling stress annealing can improve the plasticity of the welded joint and obtain better comprehensive mechanical property.
【學(xué)位授予單位】：重慶大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TG457.1;TG339
[Abstract]:As the light metal structure material, the magnesium alloy has the advantages of high specific strength, shock absorption, strong electromagnetic shielding property, easy cutting and processing, easy recovery and the like, and has great application potential in the fields of automobile, electronics, aerospace and national defense and military industry. however, the melting point and the ignition point of the magnesium alloy are relatively low, the chemical property is active, and the problems of air holes, coarse crystals and the like in the welding process are easy to occur, in particular, the mechanical property of the magnesium alloy welding joint is generally poor, the mechanical property of the magnesium alloy welding joint is generally poor, and the welding joint of the magnesium alloy is far from the parent material, The development and application of the magnesium alloy are severely restricted. In this paper, the AZ31 magnesium alloy and the AZ80 magnesium alloy with double-side TIG welding are used as the research object, and the welding is carried out on the AZ31 magnesium alloy and the AZ80 magnesium alloy, which mainly comprises the following high rolling and heat treatment. In this paper, by means of experiment and simulation, the deformation characteristics of the weld residual high rolling process are analyzed, the non-heat-treated reinforced AZ31 magnesium alloy and the heat-treated reinforced AZ80 magnesium alloy are studied, and the microstructure and the welding hole in the post-welding process are characterized by mechanical property evolution, and the strengthening mechanism. The main research results are as follows: (1) The simulation results show that the strain distribution on the welded plate is not uniform during the high rolling process, and it is divided into the bite zone, the stable deformation zone and the plate-to-roll zone, and the strain distribution is closely related to the rolling reduction. The residual high rolling can not only deform the weld zone, but also cause indirect deformation of the peripheral area of the weld, and the deformation zone can be deformed and strengthened, and the dynamic recrystallization and the refining of the tissue can also be stimulated in the case of thermal deformation. (2) The tensile strength and the elongation of the AZ31 magnesium alloy welded joint increase with the increase of the rolling reduction. When the pressing amount reaches a certain value, the tensile fracture position is transferred to the mother material by the welding line, and the tensile property of the welded joint is almost the same as that of the mother material. The local deformation strengthening of the welding area is the main strengthening mechanism in the process of high-temperature rolling of the AZ31 magnesium alloy, and the mechanical property of the AZ31 welding joint can be greatly improved by rolling at room temperature, but the weld area is easy to crack after the rolling reduction exceeds 20%. the deformation temperature is increased, the plasticity of the welding joint can be obviously improved, the rolling and cracking tendency of the welding seam is reduced, the deformation strengthening effect is weakened at the same time, the strength of the weld zone is higher than that of the parent material, and the fracture position is transferred. and (3) after the AZ80 magnesium alloy is subjected to TIG welding, a large amount of Mg17Al12 phase is generated in the weld zone, the deformation hardening effect is enhanced during the subsequent high-high rolling process, the recrystallization behavior is influenced, and the second phase of the heat-affected zone is dissolved, and the pinning effect of the Mg17Al12 relative to the grain boundary is lost, The crystal grains tend to grow abnormally during the subsequent solid-dissolving process, resulting in a reduction in the strength of the region. The reasonable composite treatment process can effectively relieve the grain growth of the heat affected zone while improving the strength of the weld zone, and fully improve the tissue performance of the magnesium alloy welding joint. and (4) the AZ80 magnesium alloy with higher aluminum content can more easily generate air holes during the welding process, and the residual high rolling process can effectively eliminate the air holes in the welding seam. with the increase of the rolling reduction, the air holes are gradually closed. When the rolling temperature is low, cracks can be generated around the air holes, which is not beneficial to the mechanical property of the welding joint, and the rolling temperature is increased, so that the plasticity of the magnesium alloy can be improved, and the occurrence of cracks is avoided. and (5) the deformation resistance of the AZ80 magnesium alloy is large, and the welding seam is easy to crack when the residual high rolling is carried out at lower than 300 DEG C, and the rolling process is difficult to carry out. In the reasonable rolling temperature range, the comprehensive mechanical properties of the AZ80 welded joint are significantly increased with the increase of the rolling reduction, the main strengthening mechanism is the deformation strengthening, the fine grain strengthening and the closing of the air holes in the welding line, and several strengthening mechanisms are best matched at the temperature of about 350 DEG C. (6) The microstructure, size and distribution of the Mg17Al12 phase in the grain boundary, the inner and outer, the deformation zone and the undeformed zone of the AZ80 welded joint are different in the process of aging after the residual high rolling. The microstructure of each region can be controlled by the post-welding composite treatment combined with the combination of the residual high rolling and the heat treatment, so as to influence the mechanical property of the welded joint. The tensile strength of the AZ80 welded joint with the welding hole is 200MPa (85% of the parent material), the tensile strength is 314MPa (88% of the mother material), and the elongation rate is 4.5% (45% of the parent material). and (7) when the residual height or the residual height of the weld can not be obtained, the magnesium alloy welding plate can be subjected to a non-residual high-temperature hot rolling, and the microstructure of each region can be refined by dynamic recrystallization, so that the grain size difference can be reduced, and the strength of the welding joint can be improved. the low-temperature short-time rolling stress annealing can improve the plasticity of the welded joint and obtain better comprehensive mechanical property.
【學(xué)位授予單位】：重慶大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TG457.1;TG339
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