A forced convection stirring process for Rheo-HPDC aluminum and magnesium alloys

Wrought Mg AZ31 alloy was near-net-shaped by semisolid rheo-diecasting. Parts with 42% and 61% solid fraction were produced at different injection velocities. The impact of injection velocity on the microstructure and the tensile strength of samples have been investigated. Results indicated that the shape factor and the particle size of primary α-Mg in the microstructure decreased with the increase of injection velocity, and the morphology of both secondary α-Mg and eutectic α-Mg + Mg17Al12 mixture were refined with the increase of injection velocity. The surface liquid segregation in the sample closely relates to the injection velocity and the solid fraction of slurries, and it decreased with the increase of injection velocity and the decrease of the solid fraction. Cold shut, crack, and gas porosity were the main internal defects that rely on the injection velocity. The tensile strength of the samples decreased with the increase of injection velocity, and the best value of 201 and 192 MPa was obtained at 0.5 m/s and 1 m/s for the sample with the solid fraction of 0.61 and 0.42, respectively. This work demonstrated a predominant effect of internal defects on the property of the rheo-diecasting (RDC) product than the microstructure; thus, defect reduction should be preferentially considered in the optimization of the RDC process.

Section: Slurry Microstructure Of the Semisolid Az31 Alloymentioning

confidence: 59%

Section: Slurry Microstructure Of the Semisolid Az31 Alloymentioning

confidence: 83%

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

Jin

Xing

Tang

et al. 2018

“…The fine spheroidal microstructure and reduced defects resulting from rheoforming primarily leads to enhanced tensile strength and elongation in the as-fabricated condition. Qi et al [73], for example, showed that compared with conventional HPDC, significantly enhanced tensile strength (543 MPa) and elongation (4.1%) of rheo-HPDC 7075 alloy after T6 heat treatment can be obtained because of the refinement of primary particles and reduction in porosity. Porosity is a destructive structural factor to any casting while the fine-grained structure contributes to an increase of yield strength due to the Hall-Petch effect.…”

Section: Tensile Behaviormentioning

confidence: 99%

Current Progress in Rheoforming of Wrought Aluminum Alloys: A Review

Gan

et al. 2020

Semi-solid processing (SSP), including rheoforming and thixoforming, offers a promising opportunity to manufacture net-shaped parts with complex structure and excellent mechanical properties. Owing to its low cost and short process, rheoforming has been the subject of extensive study over the last two decades. The interest in the rheoforming of wrought aluminum alloys is progressively growing among both the research and industrial communities. This review starts with reviewing the recent efforts and advances on preparation of semi-solid slurry of wrought Al alloys, followed by discussing the correlation between microstructure and performance of these alloys. Finally, special attention is paid in the industrial application and the future trends of rheoforming of wrought aluminum alloys.

“…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 high volume products with substantial reduction of internal porosity and improved mechanical properties of parts compared to conventional HPDC [10]. Nevertheless, due to the turbulent flow of the low solid fraction slurries in high-pressure die casting, porosity is still a problem in these castings [11] and could lead to blistering after full heat treatment [12].…”

Section: Introductionmentioning

confidence: 99%

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

Gao

Zhu

et al. 2019

Self Cite

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.