标题: 镁合金胚料显微结构对半固态成形负荷之影响
Study on the effect of magnesium alloy billet microstructure on semi-solid forming load
作者: 江维堂
Wei-Tang Chiang
徐瑞坤
Ray-Quen Hsu
机械工程学系
关键字: 镁合金;应变导引熔浆活化法;等径转角挤制;循环压缩;半固态锻造;Magnesium;SIMA;ECAE;CCDC;Semi-solid forging
公开日期: 2007
摘要: 镁合金半固态的成形方式同时拥有铸造与锻造的优点,但是要进行半固态成形需要先制备具有球状化晶粒且固液相混和均匀胚料,使得此成形方式成本大幅提高,而制造半固态胚料的方法中,以应变导引熔浆活化法(Strain Induced Melt Activation,SIMA)最为简单,也不需要昂贵设备,只需在室温下进行一定量的冷加工,再加热至半固态温度区间时,即可得到球状晶粒显微结构。传统的SIMA法利用压缩应变给予冷加工量的方法,过程中很容易造成胚料裂开,变形量受到限制。因此本研究将传统晶粒细化上使用的大量塑性变形法,应用在SIMA法中加大加工量。本研究中所选用的大量塑性变形法为等径转角挤制与循环压缩。此方法的优点在于挤制前后材料的截面积与几何形状没有太大的改变,故可重覆多次挤制,透过控制挤制温度与道次可调整材料的显微结构及机械性质。
本研究以AZ80镁合金为对象,以改良式SIMA法制备胚料,观察其半固态温度下显微组织,并进行半固态锻造探讨胚料显微组织对成形负荷之影响。实验结果显示改良式SIMA法应用在AZ80镁合金半固态胚料制备上,的确具有优良半固态成形胚料之性质,在进行半固态凸缘锻造,胚料半固态温度下的晶粒圆球化效果和平均晶粒大小为影响半固态锻造成形负荷的主要因素;晶粒形状越圆球化及平均晶粒大小越小的胚料,成形所需之负荷越小。
Semi-solid forming of magnesium alloy has the advantage of casting and forging. Semi-solid forming requires raw materials with the spheroidal grains, and homogeneous solid-liquid distribution. However, preparing billets of this kind increase costs. Strain Induced Melt Activation (SIMA) method is simple and does not require expensive equipment for preparing semi-solid billet. In SIMA method, the billet is first upset then is isothermal treated in semi-solid temperature in order to obtain spheroidal grains. However, traditional SIMA method uses upsetting process, which causes crack easily, the deformation is limited. In order to overcome the difficulties of the plastic deformation of magnesium alloys in die upset, a modified method for obtaining severe plastic deformation (SPD) was adopted. In SPD, Equal channel angular extrusion (ECAE) and channel die compression process (CCDC) are combined for obtaining ultra-fine grain. This method has the advantage of the same cross-sectional area and geometry before and after deformation. The process can be repeated for many passes. Through the control of temperature, extrusion passes, material microstructure can be modified and mechanical properties can be improved. A semi-solid forging, uses modified SIMA prepared billet was conducted, the forging loads were compared under various conditions.
In this study, magnesium alloy AZ80 was selected as the raw material, modified SIMA prepared billet, were observed of its microstructure. And semi-solid forgings of modified SIMA prepared billet were conducted. Semi-solid flange forging results indicated that shapes and grain size were main factors in relation with the forging load. More spheroidal and smaller the average sizes of the billet, the smaller forming load.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT009514517
http://hdl.handle.net/11536/38507
显示于类别:Thesis


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