【作者】 张继渊； 李元东； 李明； 邱谨； 毕广利； 管仁国；

【Author】 ZHANG Ji-yuan;LI Yuan-dong;LI Ming;QIU Jin;BI Guang-li;GUAN Ren-guo;State Key Lab.of Advanced Processing and Recycling of Nonferrous Metals, Lanzhou University of Technology;Key Lab.of Non-ferrous Metal Alloys and Processing, The Ministry of Education, Lanzhou University of Technology;Materials &Metallurgical College, Northeastern University;

【机构】 兰州理工大学省部共建有色金属先进加与再利用国家重点实验室； 兰州理工大学有色金属合金及加工教育部重点实验室； 东北大学材料与冶金学院；

【摘要】 采用自孕育法保温和未保温处理制备2024合金锭料,然后将锭料试样经热模拟机加热,部分重熔后冷却（二次凝固）。利用热模拟机加热和冷却的可控性,研究了不同冷却速度下2024合金的二次凝固组织及二次凝固行为。结果表明:锭料试样部分重熔后的凝固组织是由初生α₁颗粒、"趾状"α₂、独立的α₃颗粒和共晶组织组成;锭料原始组织对合金的二次凝固组织有明显影响;随着冷却速度的增加,α₃的大尺寸颗粒逐渐减少,小尺寸颗粒增多;α₃颗粒平均尺寸的三次方与冷却速度呈反比关系;二次凝固方式主要有两种,一种是α₂依附于α₁颗粒生长成"趾状"结构;另一种是α₃在重熔液相中独立形核并长成细小的球晶,部分球晶失稳而长成等轴晶,甚至不发达的树枝晶;共晶组织按"搭桥"方式交替生长成"层片状"或"放射状"结构,"晶内共晶"主要由"三晶交汇处"的共晶组织演变形成。更多还原

【Abstract】 The slurry of 2024 alloy prepared by self-inoculation method is isothermally held at 625℃ for 0 min and 5 min. Subsequently, the slurry is cast into ingots. The samples are heated by the thermal simulator, and then cooled to 0 ℃ at different cooling rates after partial remelting（secondary solidification）. The secondary solidified microstructure and solidification behavior of 2024 alloy after partial remelting is investigated by using the heating and cooling controllability of the thermal simulator. The results show that the solidification microstructure of 2024 ingot is made up of primary α₁ particles, "toes structure" α₂, α₃ particles and the eutectic structure after partial remelting. the secondary solidified microstructure is significantly affected by the original microstructure of 2024 alloy ingot. As cooling rate increases, α₃ for large size decreases, whereas increases for small size. The cube of the α₃ particles average size is inversely proportional to cooling rate. Secondary solidification mode includes two ways: α₂ depends on the surfaces of primary α1 particles and then grows into toes structure; α₃ independently nucleates from remelting liquid and finally grows into fine spherical particles or equiaxed dendrites. At a later solidification stage, spherical particles of α₃ are easier to merge and grow. The eutectic structure grows with bridge growth mechanism and will form a "lamellar structure" or "radiate structure". The intragranular eutectic is mainly formed from eutectic in triple grains junction.更多还原