AZ31镁合金多道次轧制板材的显微组织及力学性能

发布时间：2018-04-23 23:00

本文选题：AZ31镁合金 + 轧制　；参考：《哈尔滨工业大学》2017年博士论文

【摘要】：镁合金具有广泛的应用前景,尤其在航空、航天及汽车工业等领域,可以作为替代钢和铝合金部件的轻质材料。但是由于其密排六方的晶体结构,在室温条件下伸长率和成形性都很差,限制了其广泛的应用。因此,探索出一条既能获得良好性能,又适用于工业化生产的镁合金制备工艺,有利于促进镁合金的应用和发展。本文以目前应用最广泛的AZ31镁合金为研究对象,以最简单的双辊同步轧制为研究手段。系统研究了 AZ31镁合金铸态板坯的多道次降温热轧工艺,多道次连续温轧工艺和大道次变形量的多道次冷轧工艺。同时分析了 AZ31镁合金板材单道次轧制过程中轧制温度和道次变形量对板材的组织演化和力学性能的影响规律。详细分析了 AZ31镁合金轧制板材的微观组织(如晶粒尺寸,位错密度和孪晶等)、织构(织构强度和平均Schmid因子)对板材力学性能的影响。成功制备出屈服强度为357 MPa,抗拉强度为393 MPa的高强度AZ31镁合金板材。得到了单道次冷轧变形量大于41%并且板形良好的AZ31镁合金薄板,实现了 AZ31镁合金板材的大道次变形量冷轧工艺。通过本文的研究探索出了一条适合于工业化、大批量生产的AZ31镁合金薄板的轧制工艺路线。采用不同道次变形量(15%、20%、25%和30%)的多道次降温热轧工艺,对厚度为26 mm的AZ31镁合金铸态板坯进行开坯轧制,得到厚度为4 mm的终轧板材。轧制后得到的板材与初始铸态板坯相比,晶粒得到显著的细化,力学性能得到明显的改善。当道次变形量为30%时,轧制板材的平均晶粒尺寸最小为21.5μm,此时板材具有最高的伸长率24.7%,同时具有126.1MPa的屈服强度及242 MPa的抗拉强度。综合考虑生产效率,应优先选用30%的道次变形量进行AZ31镁合金板材多道次降温热轧实验。系统研究了轧制温度为150-300 ℃,道次变形量为10-60%的AZ31镁合金单道次轧制工艺及轧制板材的微观组织及力学性能的演化规律。随着道次变形量的增大,板材的织构类型会经历形变织构→混合织构(形变织构+再结晶织构)→再结晶织构的转变。织构强度随着轧制温度的升高逐渐减弱,而随着道次变形量的增大呈现先减小后增大的趋势。采用大的道次变形量和低的轧制温度可以获得组织更加细小的板材。当轧制温度为250 ℃时,板材的组织细化效果最明显,并且组织均匀性良好;当道次变形量在30-40%范围内时,板材具有最优的力学性能。同时成功制备出屈服强度为357 MPa,抗拉强度为393 MPa的高强度AZ31镁合金板材。分析了平均晶粒尺寸和平均Schmid因子对板材力学性能的影响,提出考虑了平均Schmid因子的Hall-Petch关系式:σ_(s-t)=(0.3/mt(σ_0+kd~(-1/2)),该公式反映了板材的组织和织构共同作用下屈服强度的变化规律。通过理论计算,量化了固溶强化,晶界强化和位错强化三种强化机制对轧制板材强度的贡献。同时分析了导致轧制板材力学性能各向异性的原因。除了织构的影响外,由于位错的分布具有方向性,垂直于该方向变形会比沿着该方向变形使位错产生更多的缠结,因此进一步影响了板材力学性能的各向异性。另外,引入了方向性因子κ = f(ε),基于实验拟合，，当κ在轧制方向取为1,在横向取为κ = 1 + 1n(h/H)时,理论计算得到的强度值与实验值符合的很好。为了进一步提高AZ31镁合金薄板的轧制效率,改善其板形质量,基于织构组织的控制,研究了 AZ31镁合金板材的大道次变形量冷轧工艺。通过设计合理的多道次降温热轧工艺及多道次连续温轧工艺,得到了织构强度很弱(仅为一般轧制板材的1/3-1/2)且大部分晶粒处于软取向的2 mm厚AZ31镁合金薄板。利用此板材进行单道次冷轧实验,最大的道次变形量可以达到41%。经过三道次冷轧,两次中间退火和一次最终退火可以获得厚度为0.55 mm,屈服强度为150 MPa,抗拉强度为300 MPa,伸长率接近20%的板形良好的AZ31镁合金薄板。使AZ31镁合金室温单道次冷轧变形量提高了近3倍,极大的提高了镁合金的冷轧生产效率。
[Abstract]:Magnesium alloys have wide application prospects, especially in the fields of aviation, aerospace and automobile industry, which can be used as light materials to replace steel and aluminum alloy components. However, because of their six square crystal structure, their elongation and formability at room temperature are very poor, limiting their wide application. Therefore, the exploration of one of them is good to obtain good results. The performance, which is also suitable for the preparation of magnesium alloys produced in industrial production, is conducive to the application and development of magnesium alloys. This paper takes the most widely used AZ31 magnesium alloy as the research object and the simplest double roll synchronous rolling as the research means. The multi pass cooling and hot rolling process of the AZ31 magnesium alloy slab is systematically studied. The multi pass cold rolling process of the continuous rolling process and the amount of the main road deformation was used. The influence of the rolling temperature and the pass deformation amount on the microstructure evolution and mechanical properties of the AZ31 magnesium alloy sheet during the single pass rolling process was analyzed. The microstructure of the AZ31 magnesium alloy rolled sheet (such as grain size, dislocation density and twin crystal) was analyzed in detail. The effect of texture (texture strength and average Schmid factor) on the mechanical properties of the plate was achieved. A high strength AZ31 magnesium alloy sheet with a yield strength of 357 MPa and a tensile strength of 393 MPa was successfully prepared. The AZ31 magnesium alloy sheet with a single pass cold rolling greater than 41% and a good plate shape was obtained, and the main road deformation of the AZ31 magnesium alloy sheet was realized. In this paper, the rolling process of a AZ31 magnesium alloy sheet suitable for industrialization and mass production is explored. A multi pass cooling hot rolling process with different pass deformation (15%, 20%, 25% and 30%) is used to roll the blank of AZ31 magnesium alloy slab with a thickness of 26 mm, and the thickness is 4 mm. Compared with the initial cast slab, the grain obtained is significantly refined and the mechanical properties are obviously improved. When the amount of the pass deformation is 30%, the average grain size of the rolled sheet is 21.5 m, the maximum elongation of the plate is 24.7%, and the yield strength of 126.1MPa and the tensile strength of 242 MPa are at the same time. Strength. In consideration of production efficiency, a multi pass cooling and hot rolling test of AZ31 magnesium alloy sheet should be selected with priority of 30% pass deformation. The single pass rolling process of rolling temperature of 150-300, AZ31 magnesium alloy with pass deformation amount of 10-60% and the evolution law of microstructure and mechanical properties of the rolled sheet are studied. The texture type of the sheet will undergo the transformation of deformation texture to mixed texture (deformation texture + RECRYSTALLIZED TEXTURE) and recrystallization texture. The texture strength decreases with the increase of rolling temperature, but decreases and then increases with the increase of the amount of pass deformation. The large amount of channel deformation and low rolling temperature are adopted. When the rolling temperature is 250 C, the microstructure refinement effect is the most obvious, and the organization uniformity is good. When the volume of the pass deformation is within the range of 30-40%, the plate has the best mechanical properties. At the same time, the high strength AZ31 magnesium alloy with the yield strength of 357 MPa and the tensile strength of 393 MPa is prepared. The influence of average grain size and average Schmid factor on the mechanical properties of sheet metal was analyzed. The Hall-Petch relation formula of mean Schmid factor was considered: sigma S-T = (0.3/mt (_0+kd~ (-1/2)). The formula reflected the variation of yield strength under the joint action of the structure and texture of the plate. The solution was calculated and the solution was quantified by theoretical calculation. The contribution of three intensification mechanisms of strengthening, grain boundary strengthening and dislocation strengthening to the strength of rolled sheet. At the same time, the reason for the anisotropy of the mechanical properties of the rolled sheet was analyzed. Besides the influence of texture, the distribution of the dislocation was directional, and the deformation in this direction would cause more tangles than the deformation along that direction. This further affects the anisotropy of the mechanical properties of the plate. In addition, the directional factor kappa = f (epsilon) is introduced. Based on the experimental fitting, when kappa is 1 in the rolling direction and when kappa = 1 + 1n (h/H) is taken laterally, the calculated strength values are in good agreement with the experimental values. In order to further improve the rolling efficiency of the AZ31 magnesium alloy sheet, the improvement of the rolling efficiency is improved. Under the control of texture structure, the cold rolling process of AZ31 magnesium alloy sheet is studied. By designing reasonable multi pass cooling hot rolling process and multi pass continuous warm rolling process, the texture strength is very weak (only 1/3-1/2 of general rolling plate) and 2 mm thick AZ31 magnesium with the most grain in soft orientation Alloy sheet. Using this sheet for single pass cold rolling experiment, the maximum pass deformation amount can reach 41%. after three pass cold rolling, two intermediate annealing and one final annealing can obtain the AZ31 magnesium alloy thin plate with thickness of 0.55 mm, yield strength 150 MPa, tensile strength 300 MPa, and elongation of close to 20%. The deformation of alloy at room temperature single pass cold rolling increased by nearly 3 times, which greatly improved the cold rolling production efficiency of magnesium alloy.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG339;TG146.22

【参考文献】