Research on AlSi7Mg Alloy Semi-Solid Billet Fabricated by RAP

doi:10.11900/0412.1961.2020.00254

Acta Metall Sin

2021, Vol. 57

Issue (6): 703-716 DOI: 10.11900/0412.1961.2020.00254

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Research on AlSi7Mg Alloy Semi-Solid Billet Fabricated by RAP

JIANG Jufu¹(

), ZHANG Yihao¹, LIU Yingze¹, WANG Ying², XIAO Guanfei¹, ZHANG Ying¹

^1.School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China
^2.School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China

Cite this article:

JIANG Jufu, ZHANG Yihao, LIU Yingze, WANG Ying, XIAO Guanfei, ZHANG Ying. Research on AlSi7Mg Alloy Semi-Solid Billet Fabricated by RAP. Acta Metall Sin, 2021, 57(6): 703-716.

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Abstract

Semi-solid metal processing is a metal-forming technology that combines the advantages of casting and forging, realizing near-net forming high-performance parts with complex structures. Research on semi-solid processing of AlSi7Mg alloys mainly focuses on rheology, and the preparation of high solid fraction AlSi7Mg semi-solid billets by the solid phase method has been largely neglected. In fact, semi-solid technology is more significant than casting at higher solid fractions. The present study investigates semi-solid billets of AlSi7Mg aluminum alloy with a high solid fraction, prepared by the recrystallization and partial re-melting (RAP) method. The effects of upsetting temperature, compression ratio, semi-solid isothermal treatment temperature, and holding time on the billet microstructure were investigated by DSC test, upsetting experiment, semi-solid isothermal treatment experiment, OM observations, and Image Pro Plus image processing software. The microstructure of the semi-solid billet during isothermal compression was slightly affected by temperature but was beneficially refined by increasing the compression ratio. The optimal hot upsetting parameters were 240^oC and 40% deformation. During the semi-solid isothermal treatment, increasing the holding temperature gradually increased the size of the solid phase grains in the microstructure. As the holding time increased, the solid phase particles in the semi-solid structure initially grew slowly, and thereafter rapidly grew to a stable size. The changes in roundness of the solid particles were more complicated. The average grain size of the billet prepared by the RAP method was 64~117 μm, and the shape factor was 0.76~0.89. The linear relationship between cubic coarsening of the average semi-solid grain size and isothermal time was nonobvious at isothermal temperatures below 599^oC but was evident at temperatures of 599^oC. Below 599^oC, the grain coarsening is affected by Ostwald ripening, coalescence, recrystallization, and melting; while at 599^oC, the grain coarsening was dominated by Ostwald ripening.

Key words: synthesizing and processing technics for material semi-solid billet recrystallization and remelting microstructure AlSi7Mg

Received: 13 July 2020

ZTFLH:

TG249.9

Fund: National Key Research and Development Program of China(2019YFB2006500);National Natural Science Foundation of China(51875124)

About author: JIANG Jufu, professor, Tel: 18746013176, E-mail: jiangjufu@hit.edu.cn

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	Jufu JIANG
	Yihao ZHANG
	Yingze LIU
	Ying WANG
	Guanfei XIAO
	Ying ZHANG

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https://www.ams.org.cn/EN/10.11900/0412.1961.2020.00254 OR https://www.ams.org.cn/EN/Y2021/V57/I6/703

Table 1 Chemical composition of AlSi7Mg aluminum alloy

Fig.1 DSC curve of AlSi7Mg aluminum alloy (a) and its liquid phase ratio-temperature curve (b)

Fig.2 Upset samples under different deformations of AlSi7Mg aluminum alloy

Fig.3 The influence of different deformation temp-eratures and deformation amounts on AlSi7Mg aluminum alloy semi-solid billet

Fig.4 OM images of microstructures with different deformation temperatures at 40% deformation of AlSi7Mg aluminum alloy semi-solid billet (isothermal temperature T = 599^oC, isothermal time t = 11 min)

Fig.5 OM images of microstructures with different deformation temperatures at 30% deformation of AlSi7Mg aluminum alloy semi-solid billet (T = 599^oC, t = 11 min)

Fig.6 OM images of microstructures with different deformation temperatures at 20% deformation of AlSi7Mg aluminum alloy semi-solid billet (T = 599^oC, t = 11 min)

Fig.7 OM images of microstructures of AlSi7Mg aluminum alloy semi-solid billet at different isothermal time (T = 581^oC)

Fig.8 OM images of microstructures of AlSi7Mg aluminum alloy semi-solid billet at different isothermal time (T = 584^oC)

Fig.9 OM images of microstructures of AlSi7Mg aluminum alloy at different isothermal time (T = 588^oC)

Fig.10 OM images of microstructures of AlSi7Mg aluminum alloy at different isothermal time (T = 593^oC)

Fig.11 OM images of microstructures of AlSi7Mg aluminum alloy at different isothermal time (T = 599^oC)

Fig.12 Scatter diagram and linear fitting diagram of D³ with isothermal time (K—coarsening rate of solid grain, R²—coefficient of determination )

Fig.13 D (a) and f (b) with isothermal temperatures in different isothermal time groups

Fig.14 D and f with different isothermal temperatures at isothermal time of 11 min

Fig.15 Comparison of microstructures of AlSi7Mg aluminum alloy semi-solid billets prepared by different methods (RAP—recrystallization and partial remeltling, MHD—magnetohydrodynamic, MITP—melt isothermal treatment process)

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