轧制对AZ31镁合金焊接接头组织和性能的影响

发布时间：2018-05-07 03:16

本文选题：镁合金 + TIG焊接　；参考：《重庆大学》2015年硕士论文

【摘要】：本研究针对镁合金焊接接头力学性能差的问题,对TIG焊的AZ31镁合金板材进行了两种不同的轧制变形:1)焊后板材整体轧制变形;2)焊后板材余高轧制。本文主要研究了轧制变形方式、变形温度、轧制压下量等因素对AZ31镁合金焊接接头的组织性能的影响。研究主要得到如下结论:①整体轧制工艺对AZ31焊接板材组织与性能的影响焊后对板材进行300℃、2h去应力退火,在轧制温度为350℃下分三道次进行轧制,每道次的总压下量分别为10%、27%和43%。通过光学显微镜、扫描电镜、拉伸试验、硬度测试,研究了镁合金TIG焊接接头在轧制前后的组织和性能变化。结果显示随着轧制的进行,熔合区、热影响区和母材的组织都发生不同程度的再结晶,当压下量达到43%时,组织发生完全动态再结晶,三个区域的晶粒尺寸趋于一致。镁合金焊接接头的抗拉强度和显微硬度都随着轧制压下量的增加呈上升趋势,当压下量为27%时,镁合金焊接接头的抗拉强度达到了同等条件下母材的抗拉强度的97%,说明此时焊接接头的性能跟母材的性能差距更小。对压下量为27%的焊后轧制板材进行180℃、1h退火处理,结果发现退火后的组织只发生了回复,无明显再结晶现象,退火后焊接板材的组织与退火前无明显变化。退火处理后抗拉强度由283MPa降低到261MPa,但是延伸率却由1.4%上升到10.9%。②焊缝余高轧制工艺对AZ31焊接接头组织与性能的影响焊后对板材进行300℃、2h去应力退火,镁合金焊接板材余高轧制主要是对有一定焊缝余高的AZ31镁合金焊接接头分别在25℃(冷轧),250℃(温轧)和400℃(热轧)下对焊缝进行不同压下量的轧制。通过光学显微镜、拉伸试验、硬度测试、宏观织构测试(XRD)以及杯突实验,发现冷轧、温轧和热轧三种情况下,熔合区组织中都出现了较多的孪晶,但温轧和热轧在压下量达到一定程度时,组织中部分开始发生动态再结晶,部分晶粒得到细化,平均晶粒尺寸减小。三种温度下的轧制板材受不同的强化机制作用,焊接接头强度、延伸率和显微硬度都随着轧制压下量增加而增大,当轧制压下量超过临界轧制压下量(当轧制压下量达到某一值时,板材的断裂位置由焊接接头转移到母材,称此时的压下量为临界轧制压下量)时,接头强度大于母材强度,断裂位置由接头转移至母材,得到冷轧、温轧和热轧的临界轧制压下量分别为20%、30%和40%。随着轧制温度升高,临界轧制压下量增大,熔合区产生更强的基面织构,根据宏观织构分布,可以得出轧制压下量对基面织构的强化作用比温度对基面织构的削弱作用明显。在杯突实验中得到,在冷轧临界压下量得到的轧制焊板的杯突值最大,强的基面织构有利于焊接接头抵抗沿ND方向的载荷,但不利于成型性能,裂纹更易萌生和扩展。
[Abstract]:In this study, in view of the poor mechanical properties of magnesium alloy welded joints, two different rolling deformation of AZ31 magnesium alloy sheet welded by TIG welding were carried out: 1) the whole rolling deformation of the plate after welding; 2) the post weld plate is high rolling. This paper mainly studied the rolling deformation mode, deformation temperature, rolling pressure and so on on the welding joint of AZ31 magnesium alloy. The main conclusions are as follows: (1) the effect of the whole rolling process on the microstructure and properties of AZ31 welded sheet is 300 C, 2h stress annealing, and three pass rolling at the rolling temperature of 350, respectively. The total pressure of each pass is 10%, 27% and 43%., respectively, through the optical microscope, scanning electron microscope, The change of microstructure and properties of magnesium alloy TIG welded joint before and after rolling is studied by tensile test and hardness test. The results show that with the rolling process, the microstructure of the fusion zone, the heat affected zone and the parent material have different degrees of recrystallization. When the pressure reaches 43%, the tissue produces complete dynamic recrystallization, and the grain size of the three regions tends to be tending. The tensile strength and microhardness of the welded joint of magnesium alloy increase with the increase of rolling pressure. When the pressure is 27%, the tensile strength of the welded joint of magnesium alloy reaches 97% of the tensile strength of the parent material under the same condition. It shows that the welding joint is less than the parent material at this time. The reduction of the welding joint is 27%. The post weld rolled sheet was annealed at 180 C and 1H. It was found that the structure after annealing had only a recovery and no obvious recrystallization. The microstructure of the welded sheet after annealing had no obvious change before annealing. The tensile strength decreased from 283MPa to 261MPa after annealing, but the elongation rate increased from 1.4% to 10.9%.. The influence of art on the microstructure and properties of AZ31 welded joint is 300 C and 2H stress annealing. The residual high rolling of magnesium alloy welded sheet is mainly rolling the weld of AZ31 magnesium alloy welded joint at 25 degrees C (Leng Zha), 250 C (warm rolling) and 400 C (hot rolling). Microscopes, tensile tests, hardness testing, macro texture testing (XRD) and cup process experiments have found that there are more twins in the fusion zone under three conditions of cold rolling, warm rolling and hot rolling, but when the rolling and hot rolling reach a certain degree, the dynamic recrystallization occurs in the middle part of the tissue and some grain is refined and the average grain is obtained. The size of the rolling plate under three kinds of temperature is affected by different strengthening mechanism. The strength, elongation and microhardness of the welded joint increase with the increase of the rolling pressure. When the rolling press exceeds the critical rolling pressure, the fracture position of the plate is transferred from the welded joint to the parent when the rolling press reaches a certain value. The strength of the joint is more than the critical rolling pressure. The strength of the joint is greater than the strength of the parent material. The fracture position is transferred from the joint to the parent material. The critical rolling pressure of the rolling and hot rolling is 20%, 30% and 40%., respectively, with the increase of the rolling temperature, the increase of the critical rolling pressure and the stronger base texture in the fusion zone, according to the macroscopic texture. It can be concluded that the strengthening effect of rolling pressure on the texture of the base surface is more obvious than that of temperature on the texture of the base surface. In the cup process experiment, the glass process value of the rolled welding plate obtained at the cold rolling critical pressure is the largest. The strong base surface texture is beneficial to the welding joint resistance to the load along the ND square, but it is not conducive to the molding performance, and the crack is more easy. Sprout and expansion.

【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG335;TG407

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