Macro-Segregation and Microstructural Characteristics in Rheo-Diecasting of a High Strength Al–4.8 mass%Si–0.7 mass%Mg Alloy

Abstract

Rheo-diecasting with electro-magnetic stirring has been carried out to investigate macro-segregation and microstructural characteristics of a high strength AlSiMg alloy under various process conditions. The amount of initial heterogeneous nucleation and the degree of temperature uniformity in the slurry are dependent on the superheat of the melt at pouring into the slurry making vessel. The formation of macro-segregation in rheo-diecasting was closely related to the microstructural characteristics of semi-solid slurries. Slurries which have fine and globular ¡-Al particles prevent the formation of macro-segregation throughout the rheo-diecast specimens. However, coarse and non-globular ¡-Al particles result in the formation of macro-segregation, leading to a non-uniform hardness distribution, dependent on the thickness of the product. Various casting process parameters were examined to prevent the formation of macro-segregation, and the optimal ranges of the process conditions for rheo-diecasting were determined as follows: the injection velocity of 0.31.0 m·s ¹1 and the mold temperature above 150°C.

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

“…In the experiment, we found that this segregation within the same sheet sample was nearly changeless along the flow direction. The distribution of the primary phase, namely the macrostructural uniformity, is also an important factor effecting the final property of the castings [21,22]. Therefore, the distributions of primary α-Mg in the cross-sections of the samples have also been investigated.…”

“…At the same velocity, when the solid fraction was increased to 0.61 (Figure 10c), a more serious α-Mg segregation along the sample thickness formed, and the width of the segregation layer was approximately 0.8 mm. However, when the injection velocity was increased to 3 m/s (Figure 10b), the distribution of primary α-Mg along the sample The distribution of the primary phase, namely the macrostructural uniformity, is also an important factor effecting the final property of the castings [21,22]. Therefore, the distributions of primary α-Mg in the cross-sections of the samples have also been investigated.…”

Macro-Segregation Characteristics in Semi-Solid Forging of a High Strength Al-4.8Si-0.7Mg Alloy

“…7,8) In semi-solid metal forming, the final solidification microstructures are greatly dependent upon the microstructures of semi-solid slurries, which are closely related to the superheat of the melt in making slurries. 15) Three types of semi-solid slurries which are shown in Fig. 2(a)(c) were used in semi-solid forging to investigate the influence of microstructures of semi-solid slurries on the formation of macro-segregation.…”