Cooling Behavior and Microstructure of Semisolid A201 Aluminum Alloy Prepared by the SEED Process

Junzhen Gao,Yonglin Kang,Qiang Zhu,Xiaogang Hu,Daquan Li

doi:10.3390/met9090922

Abstract

The biggest challenge in semisolid processing of high-performance aluminum alloys is the narrow temperature processing windows of these alloys, and as a result, the preparation of qualified semisolid slurries is very important. High solid fraction slurries of high-strength A201 alloy were prepared by the Swirled Enthalpy Equilibration Device (SEED) process. The cooling behavior and microstructures of the A201 slurries produced by the standard, as well as a modified, SEED process were investigated. The results show that qualified A201 slurry can be produced by decreasing the pouring temperature and controlling the processing time in the SEED process. The modified SEED process significantly reduced the radial temperature gradient of the melt, due to the slow cooling rates involved, with the resulting slurries being more uniform, with more spherical microstructures, as compared to those produced by the standard SEED process. The formation of the nondendritic grain structure in the SEED process is attributed to the uniformly distributed large number of nuclei within the melt and the slow cooling of the melt in the containing crucible.

Highlights

Semisolid processing (SSP) is commercially a relatively new metal-forming technology, it was first introduced in the early 1970s, which competes directly with conventional casting and/or die-casting processes to produce near-net-shape components
SSP can be divided into two major routes: rheocasting, which involves forming the semisolid slurry of nondendritic microstructure directly from a controlled partially solidified melt in one single step, and thixoforming, which involves processing the melt in a separate stage, solidifying the melt completely, and reheating the slugs back into the semisolid state, followed by the forming operation [1,2,3,4]
The primary aim of this study is to develop a modified Swirled Enthalpy Equilibration Device (SEED) process to improve the quality of prepared semisolid slurries and the processability of high-performance alloys, improving the SEED

Summary

Introduction

Semisolid processing (SSP) is commercially a relatively new metal-forming technology, it was first introduced in the early 1970s, which competes directly with conventional casting and/or die-casting processes to produce near-net-shape components. The thixoforming route belongs to the high solid fraction processes, while most of the rheocasting routes used, such as the gas-induced semisolid (GISS). Rheocasting [6], new rheocasting (NRC) [7], air-cooled stirring rod (ACSR) process [8], forced convection stirring (FCS) [9], and so forth, are low solid fraction processes. Several low solid fraction rheological high pressure die casting (Rheo-HPDC) processes have been industrialized, producing high volume. Metals 2019, 9, x FOR PEER REVIEW high volume with substantial reduction of internal porosity and improved mechanical products with products substantial reduction of internal porosity and improved mechanical properties of parts properties of conventional parts compared to conventional HPDCdue [10]. ToNevertheless, the turbulent flow of the the turbulent low solid fraction the low solid fraction slurries in high-pressure die casting, porosity is still a problem in these castings slurries in high-pressure die casting, porosity is still a problem in these castings [11] and could lead to [11]

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