【作者】 仇治勤；

【导师】 陈振华；

【作者基本信息】 湖南大学 ， 材料加工工程， 2008， 硕士

【摘要】 作为最轻的金属结构材料,镁合金特别是变形镁合金以其优异的综合性能表现出极其广阔的应用前景,高性能镁合金板材的研制已成为当今材料领域的研究热点。但常规轧制镁合金板材形成的强烈基面织构严重制约了镁合金板材的二次成形能力,因此,本文运用105o夹角模具采用等径角轧制工艺成功制备出AM60镁合金板材,分析了其经过等径角轧制之后微观组织和力学性能的变化,并对其进行了退火热处理,为制定合理的热处理工艺作参考。与普通轧制板材相比,研究结果表明:(1)等径角轧制后,AM60镁合金板材中产生了大量的孪晶并且有细密排列的孪晶生成,晶粒得到了细化,平均晶粒度由10μm左右下降到5μm左右,晶粒形状不规则,为典型的大变形组织。(2)等径角轧制后,AM60镁合金板材内晶粒c轴向轧制方向偏转了较大的角度,向非基面晶粒取向转变,改变了普通轧制板材强烈的(0002)基面织构,非基面织构的形成对板材二次成形有利。(3)等径角轧制后,晶粒细化,细密孪晶生成以及非基面晶粒取向都对流变行为产生了影响,晶粒细化,晶界协调变形能力增加,强度增大,塑性得到提高,应变硬化能力大大加强,尤其是沿轧向方向;沿轧向和横向的抗拉强度分别由轧制前的222MPa和268MPa增加至轧制后的372MPa和380MPa;沿轧向和横向的屈服强度由轧制前的156MPa和188MPa分别增加至轧制后的260MPa和265MPa。(4)退火处理后,晶粒趋向于均匀并等轴化,有条状晶粒出现,随着退火时间的延长,晶粒开始长大,孪晶逐渐消失,退火60分钟后,孪晶基本消失,条状晶粒趋于等轴化,晶界平直化,多为夹角约120°的三叉晶界,部分晶粒已经长大,但仍有细小晶粒存在。(5)退火处理后,晶粒长大、细密孪晶逐渐消失以及位错密度下降使板材的抗拉强度和屈服强度降低,但是晶粒的均匀等轴化使板材的塑性增强,断裂延伸率大大提高;另外,退火处理后,各晶面衍射峰强度有所降低,但等径角轧制所形成非基面晶粒取向依然存在,并没有从根本上改变等径角轧制AM60镁合金的非基面晶粒取向;观察到300℃×30min退火处理效果较好。更多还原

【Abstract】 Increase usage of magnesium components in the industries has propelled considerable research interest on the development of magnesium alloy,especially deformation magnesium alloy with excellent composite properties. However,the secondary deformation abilities are badly restricted by the (0002) basal texture of magnesium alloy sheets with normal rolling. Therefore,Mg-6%Al-0.5%Zn-0.5%Mn (AM60) alloy was subjected to Equal Channel Angular Rolling(ECAR)processing with 105omodul at 400℃. Microstructure observations and mechanical properties were carried out using optical microscope and tensile was tested. Annealing treatments were carried out with different periods. The study shows that(1) Twins refinement are observed in AM60 magnesium alloy with ECAR and the grain size decreases. The grain size is 10μm and 5μm before and after ECAR. The grain shapes of ECAR AM60 magnesium alloy sheet are not regular. Typical severe plastic deformation microstructure appeares.(2) It is found that the“c”axis orientation of the sheet processed by ECAR is changed and the crystal orientation evolves from (0002) basal plane orientation to non-basal plane. Non-basal texture of grains appeares. The existence of non-basal texture is advantageous to secondary deformation.(3) The rheological behavior is affected by refined grains and non-basal texture. The rheological behavior after ECAR changes obviously especially along rolling direction. The grain boundary deformation ability gets enhanced after ECAR,strength and plasticity of ECAR AM60 sheets get enhanced too,the ultimate tensile strength increases from 222 to 372 MPa and the yield strength increases from 156 to 260 MPa along rolling direction,the ultimate tensile strength increases from 268 to 380 MPa and the yield strength increases from 188 to 265 MPa along transverse direction.(4) Symmetrical axis grains and shape grains appeare after annealing treatment. Grains begin to grow up,twins begins to disappear with the annealing time going on. After 60 minutes annealing treatments,the grain boundary with 120o appears and shape grains begin to be symmetrical axis grains.(5) Sheet strength decreases after annealing treatments,because grains grew up and twins refinement began to disappear. The decreased density of the locations makes the strength low too. Twins decreases but symmetrical axis grains appeares after annealing treatment. So,strength decreases,plasticity get enhanced more. The amounts of the twins decrease obviously but the non-basal orientation of the grains processed by ECAR changes little. The effect of annealing treatments with 30 minutes at 300℃is observed better in our results.更多还原