Solid State Phenomena Vols. 141-143

Abstract: The preparation of semi-solid slurry of hypereutectic Al-Si alloy by Ultrasonic Vibration (USV) has been studied. The A390 alloy melt was poured into a preheated metal cup, and subsequently the ultrasonic vibrator was dipped into the melt and USV was imposed. The solidified microstructure of the slurry has been analyzed, and the mechanical properties of the alloy have been tested by making samples through diecasting of the slurry. The results show that the primary Si particles of A390 alloy became finer, rounder and uniformly distributed in microstructure of A390 alloy slurry if imposed with USV, and average diameter of primary Si particles was about 20μm. With USV, the ultimate tensile strength and the hardness of rheo-casted samples increased by over 25% and near 50% respectively besides the elongation rose by above 100%. After heat treatment, the mechanical properties were further improved. In addition, the mechanism of preparation of semi-solid slurry of hypereutectic Al-Si alloy by USV is discussed.

Abstract: CSIR-Rheo technology process which involves the preparation of metal slurry direct from liquid alloys by stirring and cooling was applied for treatment of Al-7%Si-0.35%Mg alloy, A356, to the Semi-Solid Metal state. Plates were cast in steel moulds with a 50 Ton High Pressure Die Casting machine. Heat treatments T4 and T6 were given to the samples. Butt laser welding was performed on the heat treated and as fabricated plates (F). Tensile properties, hardness profile, microstructure of the weld, heat affected zone and base metal were examined. Some comments on outcomes of the research are included.

Abstract: The RHEOMETALTM process is a commercially used semi-solid process for production of high integrity cast components. The process differs from most other semi-solid casting processes in that temperature control is not necessary during processing and large amount of slurry with required solid fraction can be quickly produced. The simplicity of this process has led to a large commercial interest during the last year. This work is based on an investigation regarding the variation of as-cast mechanical properties for secondary Al-Si based alloys (~2.5 % Cu) with a Si content varying from 4.55 to 8.90 % using the RHEOMETALTM process. The purpose was to find the most suitable Al-Si alloy for rheocasting, in comparison with the common HPDC-alloy A380 (EN-AC46000). It was found that lower Si containing alloys exhibited better elongation but slightly lower yield strength. The alloy containing 5.39 wt% Si showed the highest ultimate tensile strength in this investigation. The lower Si containing alloys also demonstrated better feedability in the rheocasting process, which is contrary to what normally is found for normal liquid casting processes. Based on the results in this investigation it is recommended to use an alloy containing about 5-7 wt% Si for rheocasting purposes.

Abstract: Continual improvement of product quality has been a long challenge to Semi-Solid Metal (SSM) technology. By conventional semi-solid processes, this might be attained at the expense of economical production. The advent of Inclined Cooling Plate (ICP) process has already realized the development of non-dendritic SSM while satisfying qualitative, quantitative and economical requirements collectively. In spite of its potential advantages, functional mechanisms of this process are not yet clearly understood that makes its optimal utilization obscured. Basically, such understanding needs a picture of the process. As the first step, this picture is pursued through physical modeling of the ICP process i.e. direct observation of an analog system by virtue of transparent character of a model alloy (succinonitrile-acetone). Based on this phenomenological model, a picture of the process is presented as follows: flowing molten alloy down ICP, multiple regions form typically on the plate i.e. a chilled layer at the vicinity of the plate surface, a two-phase mushy zone on the chilled layer and ambient liquid far from the plate surface. In this process, interaction of the liquid forced-flow with mushy zone separates solid particles from the stationary mush on the plate resulting in a two-phase mixture which is responsible for the formation of slurry i.e. SSM.