MICROSTRUCTURES AND PROPERTIES OF AZ91D MAGNESIUM ALLOY PRODUCED BY FORCED CONVECTION MIXING RHEO-DIECASTING PROCESS

doi:10.11900/0412.1961.2014.00523

Acta Metall Sin

2015, Vol. 51

Issue (6): 668-676 DOI: 10.11900/0412.1961.2014.00523

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MICROSTRUCTURES AND PROPERTIES OF AZ91D MAGNESIUM ALLOY PRODUCED BY FORCED CONVECTION MIXING RHEO-DIECASTING PROCESS

Mingfan QI,Yonglin KANG(

),Bing ZHOU,Guoming ZHU,Huanhuan ZHANG

School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083

Cite this article:

Mingfan QI, Yonglin KANG, Bing ZHOU, Guoming ZHU, Huanhuan ZHANG. MICROSTRUCTURES AND PROPERTIES OF AZ91D MAGNESIUM ALLOY PRODUCED BY FORCED CONVECTION MIXING RHEO-DIECASTING PROCESS. Acta Metall Sin, 2015, 51(6): 668-676.

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Abstract

Based on the forced convection mixing (FCM) principle, a self-developed FCM semisolid slurry preparation device was successfully developed. Taking AZ91D magnesium alloy tensile parts for example, the rheo-diecasting process that consists of slurry preparation, transportation and forming was achieved by combining with a diecasting machine. Microstructural characteristics of FCM rheo-diecasting parts in different processing parameters were investigated. Mechanical properties of AZ91D alloy parts in different processes were compared. Besides, the formation mechanism and solidification behavior of semisolid slurry were analyzed in FCM rheo-diecasting process. The results show that processing parameters have a great effect on the microstructures of parts, increasing rotation speed or decreasing barrel temperature appropriately is beneficial to optimizing the microstructure. The process not only can produce parts with fine, spherical and uniformly distributed primary a-Mg particles, but also is able to improve mechanical performance of parts significantly. Compared with traditional diecasting, the yield strength remains unchanged, but the ultimate strength and elongation are increased by 12.5% and 80.0%, respectively. Furthermore, compared with parts subjected to T4 and T6 heat treatment, the ultimate strength of the as-cast is the lowest, and the yield strength and elongation are between T4 and T6.

Key words: AZ91D magnesium alloy forced convection mixing (FCM) rheo-diecasting microstructure evolution mechanical properties heat treatment

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	Mingfan QI
	Yonglin KANG
	Bing ZHOU
	Guoming ZHU
	Huanhuan ZHANG

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https://www.ams.org.cn/EN/10.11900/0412.1961.2014.00523 OR https://www.ams.org.cn/EN/Y2015/V51/I6/668

Fig.1 Structure diagram of forced convection mixing (FCM) machine (a) and schematic diagram of FCM rheo-diecasting process (b) (1—slurry outlet, 2—graphite blockage, 3—emptying core bar, 4—heating and cooling elements, 5—inner barrel, 6—graphite lining, 7—spiral stirring rod, 8—insulation, 9—funnel, 10—graphite insulation ring, 11—bearing block, 12—gear, 13—adjusting handle, 14—emptying handle, 15—bearing, 16—adjustable bracket)

Fig.2 Schematic diagram of the FCM rheo-diecasting tensile test sample (unit: mm)

Fig.3 OM images of AZ91D alloy rheo-diecasting parts under rotation speeds of 100 r/min (a), 300 r/min (b), 500 r/min (c) and 700 r/min (d)

Fig.4 Mean size and shape factor of primary a-Mg particles in AZ91D alloy rheo-diecasting parts under different rotation speeds at barrel temperature of 560 ℃

Fig.5 OM images of AZ91D alloy rheo-diecasting parts under barrel temperatures of 560 ℃ (a), 570 ℃ (b) and 580 ℃ (c)

Fig.6 Mean size and shape factor of primary a-Mg particles in AZ91D alloy rheo-diecasting parts under different barrel temperatures at rotation speed of 500 r/min

Table 1 Mechanical properties of AZ91D alloy parts in different processes

Fig.7 SEM images of AZ91D alloy rheo-diecasting parts after T4 heat treatment (a) and T6 heat treatment (b)

Fig.8 Fractographs of AZ91D alloy tensile parts for traditional diecasting (a), FCM rheo-diecasting (b), T4 heat treatment (c) and T6 heat treatment (d)

Fig.9 Schematic diagrams of traditional crystal dissociating (a) and crystal dissociating in FCM device (b)

Fig.10 Solidification process of the melt in traditional diecasting and FCM rheo-diecasting

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