Microstructural Evolution During Homogenization of Direct-Chill-Cast Al–Zn–Mg–Cu Alloy

IF 3.3 3区材料科学 Q2 MATERIALS SCIENCE, MULTIDISCIPLINARY

Metals and Materials International Pub Date : 2024-10-16 DOI:10.1007/s12540-024-01814-6

Seonghyun Park, Junho Lee, Junhyub Jeon, Sang-Hwa Lee, Jung Ho Shin, Sangmin Choi, Seok-Jae Lee, Jae-Gil Jung

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Abstract

We investigated the microstructural evolution during homogenization of a large direct-chill (DC)-cast AA7050 billet. The as-cast billet consists of Al/η-Mg (Zn, Cu, Al)₂ eutectic, Mg₂Si, and Fe intermetallic compounds and exhibits higher constituent phase fraction and solute segregation and larger microstructures in the center region. As the homogenization temperature increased, the secondary phase dissolution rate and solute homogenization rate increased. The center region with larger grain size and dendrite arm spacing exhibited a sluggish rate of phase dissolution and solute homogenization. At 475 °C, a transformation from η into S phase with an orientation relationship was observed in the Al/η-Mg (Zn, Cu, Al)₂ eutectic. The η into S phase transformation did not occur at homogenization temperatures of 485 and 500 °C. Instead, an incipient melting of the Al/η eutectic occurred, resulting in formation of a rosette microstructure composed of fine Al/η eutectic and θ-Al₂Cu phases during quenching. The incipient melting region transforms to an Al matrix or porosity as alloying elements diffuse into the adjacent Al matrix. The hardness of the homogenized billets increased due to dissolution of the constituent phase but decreased as porosity due to the incipient melting becoming severe. The optimal homogenization process for the DC-cast AA7050 billet is discussed in terms of phase dissolution, solute homogenization, and incipient melting.

Graphical Abstract

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直铸Al-Zn-Mg-Cu合金均匀化过程中的组织演变

研究了直冷铸造AA7050大方坯在均匀化过程中的组织演变。铸态方坯由Al/η-Mg (Zn, Cu, Al)2共晶、Mg2Si和Fe金属间化合物组成，具有较高的组分相分数和溶质偏析，中心区域组织较大。随着均质温度的升高，二相溶解速率和溶质均质速率均增大。晶粒尺寸和枝晶臂间距较大的中心区域，相溶解和溶质均质化速度较慢。在475℃时，Al/η- mg (Zn, Cu, Al)2共晶由η相转变为S相，并伴有取向关系。在485℃和500℃的均质温度下，η到S相的转变没有发生。相反，Al/η共晶在淬火过程中开始熔化，形成了由Al/η共晶和θ-Al2Cu相组成的玫瑰花状组织。当合金元素扩散到邻近的Al基体中时，初熔区转变为Al基体或孔隙。均匀化后的钢坯硬度由于组成相的溶解而增加，但由于早期熔化变得严重而导致孔隙率降低。从相溶、溶质均匀化和初熔三个方面讨论了直流铸造AA7050坯料的最佳均匀化工艺。图形抽象

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来源期刊

Metals and Materials International 工程技术-材料科学：综合

CiteScore

7.10

自引率

8.60%

发文量

197

审稿时长

3.7 months

期刊介绍： Metals and Materials International publishes original papers and occasional critical reviews on all aspects of research and technology in materials engineering: physical metallurgy, materials science, and processing of metals and other materials. Emphasis is placed on those aspects of the science of materials that are concerned with the relationships among the processing, structure and properties (mechanical, chemical, electrical, electrochemical, magnetic and optical) of materials. Aspects of processing include the melting, casting, and fabrication with the thermodynamics, kinetics and modeling.