AM-cast is a zirconium-rich master alloy, developed to ease the process of incorporating small quantities of zirconium in magnesium alloys. Zirconium additions produce very fine grain (crystal) sizes in certain magnesium alloys, predominantly those not containing aluminium. These fine grain sizes are required to improve properties, such as strength and ductility, in sandcast and VDC billet cast magnesium alloys.
AM-cast efficiently enables the dispersion and dissolution of zirconium in molten magnesium alloys with little wastage of zirconium. The yield for both master alloy and the alloy being grain refined is much greater than for competitor master alloys.
Commercial Opportunities for AM-cast Zirconium-Rich Master Alloy
Achievement of a fine grain size generally leads to improved properties, of most metals and leads to improvements in both strength and ductility. Thus, a fine grain size in castings is important for their service performance and is also important for the end properties of semi-fabricated products, eg. such as extrusions, that are produced from cast billet. High pressure die castings generally have a fine microstructure because of the extremely high solidification rates, that are achieved in the casting process, and do not need the addition of a special grain refining agent. However, the solidification rate in sand castings, permanent mould castings and billet castings is much slower and a uniform fine microstructure can generally only be achieved in these castings by addition of a grain refining additive to the melt prior to casting.
Zirconium Containing Magnesium Alloys
It has long been known that small additions (0.5, 1%) of zirconium have an exceptional grain refining ability in magnesium alloys that do not contain aluminium. There is an important high value-added class of magnesium alloys that contain no aluminium and which are currently used in small volumes for sand cast components for the aerospace industry and other niche applications such as racing cars. These alloys are zirconium grain refined. A number of new creep resistant alloys, such as AM-SC1, for powertrain applications in the automotive industry also require zirconium grain refinement and have the potential for significant growth. A lower cost method of adding zirconium is essential for low cost production of components made from AM-SC1.
Successful Development of AM-Cast Zirconium-Rich Master Alloy
AM-cast was developed in a program of work carried out for Advanced Magnesium Technologies by CAST over the past 2 years. The key to AM-cast has been the development of methodology for dissolution and dispersion of fine particles of zirconium in molten magnesium, casting this master alloy into small ingots, and a subsequent method for adding the master alloy to magnesium alloys prior to casting. AM-cast contains a very fine dispersion of zirconium particles that are less than 10 microns in size and which are ideal for grain refinement of a number of high strength magnesium alloys. An important advantage of AM-cast over competing technologies, is that its usage drastically reduces wastage in the form of metal dross and sludge in customer foundries and thus contributes markedly to a reduction of costs in foundries. AM-cast has been shown to achieve the same results for one third of the weight of its competitors master alloys. Zirconium grain refiners typically sell for around $45,000 per tonne and more.
Patents for AM-cast Technology
International patents covering the AM-cast technology have been applied for. As for all the other products it has developed with CAST, Advanced Magnesium Technologies has the exclusive worldwide rights to commercialise this technology.
Current Status of AM-Cast Zirconium-Rich Master Alloy
The advantages of AM-cast have been demonstrated in foundry trials in Germany and USA and the master alloy is now being test marketed on a wider scale. Apart from its obvious advantages as a grain refining master alloy for use by sandcasting foundries, AM-cast is also particularly well suited for the grain refinement of certain alloys that are cast as billets, or slab, by the semi-continuous direct chill (DC) casting process. This opens up new opportunities for development of improved magnesium alloys, billets and slab intended for further processing by extrusion and rolling operations. An initial (DC) casting trial, utilising AM-cast, to produce billet for extrusion was recently conducted in a European facility. Billet produced in this trial has subsequently been extruded very successfully extruded in a commercial facility and showed excellent properties in the finished product.