Development of a Nucleation-Accelerated-Semisolid-Slurry-Making Method and its Application to Rheo-diecasting of ADC10 Alloy

Abstract

A new slurry-making method, called the nucleation-accelerated semi-solid slurry (NASS) method, was developed to fabricate high-quality semi-solid slurry with fine and uniform globular microstructures. The method's application to rheo-diecasting of ADC10 alloy was investigated. To enhance the heterogeneous nucleation of primary a particles in the initial stage of solidification, various types of funnels, including the pouring system in the slurry-making vessels, were designed and estimated by thermal analysis. It was found that the heterogeneous nucleation of primary a particles was closely related to the temperature-time history and the flow pattern. In the present study, the NASS method was set up based on the optimized funnel. It consisted of a specially designed conical-shaped funnel and the electromagnetic stirring (EMS) unit for artificial agitation. The conical-shaped funnel generated swirly flow pattern in the melt. This was further exaggerated by the EMS in the slurry-making vessel during the pouring stage, resulting in a copious heterogeneous nucleation. The qualities of the slurry were investigated using optical microscopy and rheodiecasting. To study the effect of process parameters, the semi-solid slurry of ADC10 alloy was rheo-diecast using an 85-ton high-pressure die casting (HPDC) machine. Microstructural observation and hardness test were then carried out on the rheo-diecast specimens. The rheo-diecast products of the NASS method showed fine and uniform microstructures, with primary a-globules diameter averaging 39 mm and form-factor indicating a degree of globularity of 0.9. The optimized heat treatment condition for the rheo-diecast product of ADC10 alloy was achieved at the solution temperature of 490°C for 30-60 min, water quenching, and age hardening at 180°C for 7-8 h.

Application of Rheo-diecasting of a High Strength Al^|^ndash;Si^|^ndash;Mg Alloy to Automotive Suspension Arms

“…The amount of heterogeneous nucleation can be estimated by the recalescence temperature, referred to as ΔT R , as caused by the latent heat of solidification. 10) As shown in Figs. 2(a) and 2(b), the recalescence temperatures on the bottom surface of the vessel (ΔT R sur) were larger than those at the center of the slurry vessel (ΔT R cen), and the ΔT R sur with EM stirring was much larger than that without EM stirring.…”

“…10,13) The quality of semi-solid slurries is closely related to the size and the density of the globular α -Al particles, which are dependent on the stirring conditions and the size of the slurry-making vessel. In order to obtain fine and uniform globular microstructures, it is necessary to increase the number of heterogeneous nucleation sites and to control the temperature and solute fields uniformly in the melt during the formation of slurries.…”

“…In our previous studies, electromagnetic stirring was successfully applied to manufacture high quality semi-solid slurries using AC4C and ADC10 alloys, which have fine and globular α-Al particles. 10,11) The new alloy developed in our previous study was based on Al-5.0wt%Si-0.7wt%Mg in order to improve the mechanical properties. The amount of Si is generally known to be closely related to the fluidity of semi-solid slurries in the die cavity during rheo-diecasting.…”

Development of a High Strength Al-Si-Mg Alloy for Rheo-diecasting

“…전자기 교반(Electromagnetic Stirring; EMS)을 접목한 레오 다이캐스팅은 주조조직의 미세화로 강도, 인성 등이 우수하고, 열처리를 통한 강도의 향상을 도모할 수 있으며, 일반적인 다이 캐스팅 합금 전반에 적용이 가능하여 고강도 특성을 필요로 하 는 제품 전반에 도입이 가능 할 것으로 기대된다 [7,8] …”

Effects of Two Stages of Electro-Magnetic Stirring on Microstructural Evolution in Rheo-Diecasting of a Near Eutectic Al^|^ndash;Si Alloy

“…[5][6][7][8] In rheocasting, fine and globular primary α-Al particles can be obtained instead of forming α-dendritic microstructure in solidification of Al-Si alloys. According to the previous studies, [9][10][11] fine and uniform α-Al globular microstructure, called semi-solid slurry, can be obtained by EM stirring during primary solidification. An advanced rheo-diecasting process, using semi-solid slurry making process coupled with diecasting, is now in the stage of mass production of automotive parts based on A356 (Al7Si0.25Mg) and ADC10 (Al9Si3Cu) alloys.…”