Rheo-Cast Microstructure and Mechanical Properties of AM60 Alloy Produced by Self-Inoculation Rheo-Diecasting Process

Abstract

Rheo-forming is becoming the choice for production of high quality parts with diminished defects and fine integrity. In this paper, the novel self-inoculation rheo-diecasting (SIRD) process, in which semisolid slurry is produced by mixing two precursory solid and liquid alloys and subsequently pouring them through a multi-stream fluid director, has been proposed. Microstructural characteristics of AM60 alloy slurry and the microstructure and mechanical properties of rheo-diecasting AM60 samples were investigated. Quenching experiments reveal that the slurry microstructure of AM60 was well refined to irregular α-Mg particles with the average size of approximately 20-40 µm after pouring with the self-inoculation process, and these particles were evolved to globular and coarse morphology while continuously keeping in semisolid state. After rheo-diecasting, the microstructure of the sample was dominated by fine primary α-Mg globules accompanied with tiny secondary α-Mg particles while the sample from conventional liquid die casting was characterized by developed dendrite and porosity. Microscopic analysis indicates that there are three stages of remaining liquid solidification in die cavity in SIRD: α-Mg nucleation and growth on primary α-Mg surface, α-Mg nucleated independently in liquid, and, finally, formation of skeleton devoiced eutectic. Due to diminished porosity and hot tearing, tensile strength and elongation of SIRD samples were increased by 12.9% and 35.3%, respectively, compared to a conventional liquid die casting sample.

Creep behaviour of different microstructural zones of TIG-welded semisolid cast AXE622 alloy

“…The relatively small grain size in the FZ can be due to the cooling rate, which is much faster in HAZ than in other regions [6]. Moreover, the incoming heat from the FZ causes the temperature rise in the HAZ (to about 527 K) [8], which may be more than the recrystallisation temperature of the Mg alloys, leading to substantial grain growth and the largest grain size in the HAZ.

Figure 1 Optical micrographs of (a) BM, (b) HAZ, (c) FZ.

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“…The theoretical melting temperature of the present alloy was obtained, based on the JMatPro calculation software, as 610°C. The melting temperature of similar Mg alloys such as AM60 [8] and AZ91 are 615°C and 673°C [9], respectively. Moreover, the melting point of the pure Mg is 651°C.…”

Rheo-Diecasting of Wrought Magnesium AZ31 Alloy and the Effect of Injection Velocity on Microstructure and Tensile Strength

“…The slurry was prepared with a self-inoculation method, which involves adding certain fraction of solid blocks of AZ31 and pouring the alloy melt through a multi-stream cooling channel. Details of this process are shown in the literature [9,10]. In this work, 1.5 kg of alloy ingots was melted in a resistance furnace.…”

“…The microstructure consisted of fine and spherical α-Mg particles, and its average size was reduced to 76 µ m. This semisolid microstructure feature, similar to cast Mg alloy of high Al content such as AZ91 and AM60 [11,12], commendably meets the requirements of semisolid forming. The authors' previous work provides detailed information of the slurry-making process [9,10]. Figure 5 shows the microstructure of the rheo-diecasted AZ31 alloy at different injection velocities.…”

Secondary Solidification Behavior of A356 Aluminum Alloy Prepared by the Self-Inoculation Method

“…Therefore, it is necessary to study the solidification behavior of the secondary particles in the remaining liquid of the slurry, the eutectic reaction and their microstructural characteristics. In view of this, based on the previous studies [19][20][21][22], the thin-walled discal casting of A356 aluminum alloy was prepared by combining the semisolid slurry preparation by the self inoculation method with the traditional high-pressure die casting. The solidification behavior of the remaining liquid in rheo-diecasting of the A356 aluminum alloy was elaborated and quantitative analysis was used to investigate the secondary particles and the Si morphology in different forming positions, in order to provide a theoretical reference and technical guidance for rheo-diecasting applications of A356 aluminum alloy.…”