B Jiang

A New Technology for Treating Liquid Metals with Intensive Melt Shearing

Melt quality is crucial for both continuous and shape casting of light alloys. Gas, oxides and other inclusions in the melt usually deteriorate the quality of the casting products. Conventional refining techniques, such as filtration and rotary degassing, can refine the melt by removing the inclusions although they are costly and time-consuming. A new technology for liquid metal treatment through intensive melt shearing was developed recently to improve the melt quality prior to metal casting. The new technology uses a simple rotor-stator unit to provide intensive melt shearing, which disperses effectively the harmful inclusions into fine particles to enhance nucleation during the subsequent solidification processing. Experimental results have demonstrated that the high shear unit can be used for general melt treatment, physical grain refinement, degassing and preparation of metal matrix composites and semisolid slurries. In this paper we offer an overview of the high shear device and its application in processing light alloys.

Microstructures of DC Cast Light Alloys under the Influence of Intensive Melt Shearing

A new direct chill (DC) casting process, melt conditioned DC (MC-DC) process has been developed for production of high quality ingots and billets of light alloys. In the MC-DC casting process, intensive melt shearing provided by a newly developed rotor-stator unit is used to control the solidification process during the DC casting with a conventional DC caster. Experimental results of DC casting of Al- and Mg-alloys with and without intensive melt shearing have demonstrated that the MC-DC casting process can produce light alloy billets with significantly refined microstructure and substantially reduced cast defects. The effect of intensive melt shearing on grain refinement has been mainly attributed to the enhanced heterogeneous nucleation on well dispersed oxides occurring naturally in the alloy melt.

Grain refinement of DC cast magnesium alloys with intensive melt shearing

A new direct chill (DC) casting process, melt conditioned DC (MC-DC) process, has been developed for the production of high quality billets/slabs of light alloys by application of intensive melt shearing through a rotor-stator high shear device during the DC casting process. The rotor-stator high shear device provides intensive melt shearing to disperse the naturally occurring oxide films, and other inclusions, while creating a microscopic flow pattern to homogenize the temperature and composition fields in the sump. In this paper, we report the grain refining effect of intensive melt shearing in the MC-DC casting processing. Experimental results on DC casting of Mg-alloys with and without intensive melt shearing have demonstrated that the MC-DC casting process can produce magnesium alloy billets with significantly refined microstructure. Such grain refinement in the MC-DC casting process can be attributed to enhanced heterogeneous nucleation by dispersed naturally occurring oxide particles, increased nuclei survival rate in uniform temperature and compositional fields in the sump, and potential contribution from dendrite arm fragmentation.

Degassing LM25 aluminium alloy by novel degassing technology with intensive melt shearing

Abstract Hydrogen is the only gas that is appreciably soluble in aluminium and its alloys and is the main cause of the gas porosity in aluminium alloy castings. A novel degassing technology with intensive melt shearing and Ar injection has been developed and its degassing effect on aluminium alloy has been studied. The experimental results showed that the new degassing technology can significantly degas LM25 aluminium alloy within a quite short period of time. By applying intensive melt shearing and Ar injection of 60 s, the density index Di was reduced from 10·70 to 0·98%, which means that the hydrogen concentration in the liquid alloy was significantly reduced. The effect of degassing time and isothermal holding time after degassing on the hydrogen concentration level in LM25 alloy melt was also studied and the mechanism of high degassing efficiency with this technology was discussed.

Melt Conditioned DC (MC‐DC) Casting of Magnesium Alloys

A new melt conditioned direct chill (MC-DC) casting process has been developed for producing high quality magnesium alloy billets and slabs. In the MC-DC casting process, intensive melt shearing provided by a high shear device is applied directly to the alloy melt in the sump during DC casting. The high shear device provides intensive melt shearing to disperse potential nucleating particles, creates a macroscopic melt flow to distribute uniformly the dispersed particles, and maintains a uniform temperature and chemical composition throughout the melt in the sump. Experimental results have demonstrated that the MC-DC casting process can produce magnesium alloy billets with significantly refined microstructure and reduced cast defects. In this paper, we introduce the new MC-DC casting process, report the grain refining effect of intensive melt shearing during the MC-DC casting process and discuss the grain refining mechanism.

Degassing of LM24 Al alloy by intensive melt shearing

Abstract Hydrogen can dissolve to a significant extent in molten aluminium and is the main cause of gas porosity in castings. The effect of intensive melt shearing on hydrogen concentration in molten aluminium alloy has been studied by both reduced pressure test and direct hydrogen measurement, and the results show that intensive melt shearing has a significant degassing effect for the LM24 aluminium alloy melt. By applying intensive melt shearing, the hydrogen concentration in the liquid alloy was reduced from 0·16 to 0·08 mL/100 g, and the density index Di was reduced from 12·40 to 2·96%. It was also found that shearing speed, shearing time and holding time after shearing could influence the degassing efficiency. In addition, pressurised melt filtration was also carried out to understand the mechanism of reduced porosity by intensive melt shearing, particularly the role of oxide in the formation of porosity, and the microstructure refinement.

Improvement of mechanical properties of HPDC A356 alloy through melt quenching process.

Melt quenched high pressure die casting (MQ-HPDC) is a new die casting process developed recently for improving the casting quality of the conventional HPDC process. In the MQ-HPDC process, an alloy melt with a specified dose and superheat is quenched by directly pouring the alloy melt into a preheated metallic container. The thermal mass and preheating temperature of the container is selected so that the alloy melt is quenched just below the alloy liquidus and heterogeneous nucleation takes place during the melt quenching. The quenched alloy melt is then fed immediately into the shot sleeve for component casting. In this paper we present the MQ-HPDC process and the resultant microstructures and mechanical properties of a MQ-HPDC A356 alloy.