PDF《半固态加工——特种铸造及有色合金 2011年年会专刊——》

半固态加工――特种铸造及有色合金 2011年年会专刊―― 半固态LYl 2合金坯 料二次加 热组织控制工艺与机理 王顺成蔡畅戚文军郑开宏 (广东省工业技术研究院材料加工研究所) 摘要提出先在液相线以上某温度适当等温加热.

然后再降低温度至两相区继续等温保温的半固态坯料两步法二次加 热工艺,采用该工艺对低过热度铸造半固态LYl2合金坯料进行二次加热,研究了坯料的组织演变规律.探讨了组织控制 机理.结果表明,采用两步法加热工艺.由于坯料升温速度加快和熔化过热温度提高,可加快坯料的部分重熔和组织转变 速度,而晶间液相形成速度加快对晶粒长大具有一定的抑制作用,二次加热后坯料晶粒更加圆整和细小,坯料加热时间也 明显缩短.有利于提高坯料的二次加热效率. 关键词半固态金属;

触变成形I二次加热;

组织控制 中圈分类号 TGl46.2 文献标志码 A文章编号 2011(S)一0375―04 Control Process and Mechanism of Microstructure of Semi―Solid

2024 Alloy during Reheating Wang Shuncheng,Cai Chang,Qi Wenlun,Zheng Kaihong (Institute of Materials Processing,Guangdong GeneraI Research Institute of Industrial Technology) Abstract:A two-step reheating process was proposed and applied tO perform reheating experiments on the semi―solid

2024 alloy billet prepared by low superheat pouring.In this process,the semi―solid billet was firstly heated isothermally over liquidus temperature for a few seconds,and then held isothermally at solidus―liquidus zone temperature.The microstructure evolution of semi―solid billet during the two-step reheating process was studied and the control mechanism was discussed.The results show that the for― mation rate of liquid phase of semi―solid billet during the two-step reheating process is faster than that during the isothermal reheating process.The accelerating of liquid phase formation during the two-step reheating process can restrain the coalescence of grains tO a certain extent,and thus reduce the growth rate of grains and promote the spheroidization rate.The grains of semi―solid billet reheated by the tWO- step reheating process are finer and rounder than those by the isothermal reheating process. Key Words:Semi-solid Metal,Thixoforming,Reheating,Microstructure Controlling 半固态金属触变成形具有提高铸件致密度、延长模 具使用寿命和实现高速近终成形等优点,可应用于生产 高强度、高致密度零部件….触变成形工艺包括半固态 坯料的制备、二次加热和触变成形三个技术环节,在这 三个环节中,半固态坯料二次加热具有承上启下的作 用.通过二次加热使坯料获得一定的液相体积分数,坯 料的非枝晶组织品粒进一步球化,使坯料既具有一定强 度又具有良好的触变性能,满足触变成形工艺对坯料的 要求【2].目前常采用的二次加热工艺是在某一预定固 液两相区温度下进行等温加热工艺,科研人员先后研究 了坯料原始组织状态、加热温度和保温时间等对坯料二 次加热组织的影响及其组织转变规律【3~5].两相区等 温二次加热工艺的优点是易于通过控制加热温度获得 所需的液相率,同时,还可实现长时间的保温确保晶粒 得到充分的球化.但是在固液两相区等温加热,由于坯 料过热温度低,坯料部分重熔缓慢.加热时间较长,加热 效率低.另外,加热保温时间过长容易导致晶粒粗化, 而晶粒粗化又会降低坯料的触变性能,同时还会恶化成 形件的力学性能. 为了实现半固态坯料二次加热既满足获得所需的 液相体积分数.同时又能获得既细小又圆链的品粒组 织.以及提高坯料的二次加热效率,本课题提出先在液 相线以上某温度适当等温加热.然后再降低温度至两相 区继续等温保温的半固态坯料两步法二次加热组织控 收稿日期:2011一05―11 '