【作者】 应韬；

【导师】 郑明毅；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2009， 硕士

【摘要】 本文采用冷压-热压-热挤压和冷压-热压两种方法对AZ91镁合金车削屑进行了固相成型,并在300℃、350℃对其进行了1~4道次的ECAP变形。采用光学显微镜研究了AZ91镁屑固相成型材料ECAP变形前后的显微组织变化,采用X射线衍射对ECAP变形前后AZ91镁屑固相成型材料的织构演变进行了分析,采用拉伸试验机对ECAP变形前后AZ91镁屑固相成型材料的室温拉伸及压缩性能进行了测试,采用阿基米德法对ECAP变形前后AZ91镁屑固相成型材料的密度进行了测试。铸态和固溶态AZ91镁屑经冷压-热压后密度较小,屑与屑之间的结合并不十分紧密,还有观察到屑与屑之间的界面以及孔洞等缺陷的存在;热挤压后密度急剧增加,基本达到饱和。热挤压后晶粒度约为10μm,经过300℃1~2道次的ECAP,晶粒尺寸可以达到2~3μm。随着ECAP变形道次的增加,较大晶粒逐渐破碎,再结晶大面积发生,晶粒分布趋于均匀。随着变形温度的升高,再结晶越来越充分,晶粒逐渐趋于等轴,位错密度逐步降低。由于受到晶粒度和织构双重因素的影响,ECAP变形后AZ91镁屑固相成型材料的屈服强度随着变形道次和变形温度的升高逐渐降低,延伸率也逐步降低,这可能是由于氧化物的存在,诱发孔洞的产生,导致延伸率的下降。经过300℃1道次的ECAP,材料的屈服强度和抗拉强度相比挤压态提高了40%和25%。铸态AZ91镁屑冷压-热压后直接进行ECAP变形,材料的密度提升没有热挤压来的快,ECAP变形4道次后,材料的密度基本达到饱和。经过1~2道次的ECAP,晶粒尺寸可以达到4μm。随着变形道次的增加,较大晶粒逐渐破碎,再结晶大面积发生,晶粒分布趋于均匀,经过4道次的ECAP变形,晶粒尺寸细化到2μm。材料的屈服强度随着随着变形道次的增加先升后降,这是由于晶粒度和织构之间的竞争作用及致密度的影响。材料的抗压强度及延伸率随着道次的增加而增加,这主要是由于密度及晶粒度的影响。更多还原

【Abstract】 Two ways were used to recycle AZ91 magnesium chips in this paper. One was solid state recycling by hot extrusion and ECAP, the other is directly ECAP without hot extrusion. Equal channel angular pressing (ECAP) was performed at the temperature 300℃and 350℃for different passes. The microstructure of the ECAPed AZ91 chips were examined by means of optical microscopy (OM). Texture development of the as-extruded and ECAPed AZ91 magnesium chips were investigated by X-ray diffractometer. Tensile deformation behavior of the as-extruded and ECAPed AZ91 magnesium chips at room temperature were investigated. The densities of as-extruded and ECAPed AZ91 chips were measured by Achemide methodTwo kinds of AZ91 magnesium chips(As-cast and T4) were selected as the material for solid state recycling by hot extrusion and ECAP. After cold-press and hot-press, the density was low, this was due to the weakness of the bond between chips, but after hot extrusion, the density increased dramatically, almost achieved full density. The as-extruded chips had an initial grain size of about 10μm, after 1~2 passes of ECAP at 300℃, the grain size was refined to 2~3um. With the increase of ECAP pass, the grain sizes became more uniform.became equiaxed and dislocation density decreased. With the increase of ECAP temperature, the grains became more equiaxed and dislocation density decreased. Influenced by dual factors of grain size and texture, the yield stress of ECAPed AZ91 chips decreased with increasing of ECAP passes, and the ductility at ambient temperature was decreased because of cavitation induced by oxide from the surface of the chips. After 1 pass of ECAP at 300℃, the specimen showed about 40% higher 0.2% yield stress and about 25% higher tensile strength compared with as-extruded chips.Another way of recycling without hot extrusion was conducted on as–cast magnesium alloy chips. After ECAP, the density was increased, but not as significant as hot extrusion. After 4 passes of ECAP, full density was achieved. The grains refined to 4um and 2um after 2 passes and 4 passes respectively. The yield stress of ECAPed AZ91 chips first increased and then decreased with increasing of ECAP passes, this was due to the density and dual factors of grain size and texture. The compression strength and elongation to failure were both increased with the increase of passes, the increase of density and fine grain size maybe the reason.更多还原