Aluminum Grain Refiner Master Alloys

GENERAL:

No ImageIn casthouse applications, the control of grain size is essential in maintaining product consistency and quality, in reducing cost and maintaining high levels of productivity. Controlled addition of Al-TiB master alloy in aluminum releases nucleating particles that promote equiaxed, fine grained structures in cast alloys, thus redistricting formation of columnar crystals. Al-TiB grain refiner alloy improves homogeneity and allows uniform distribution of alloying elements, reduce porosity and eliminate hot tearing in cast structures, improves responsiveness to subsequent heat treatment and enhance mechanical properties and machinability in the fabrication process. 

There are two types of particles seen in microstructure of Al-TiB: TiB2 particles – grain refining nuclei – typically 1-2 microns in size, which do not dissolve in liquid aluminum TiAl3 plates / grains – typically 30-60 microns in size, which readily dissolved in liquid aluminum. These particles play an important role in the grain refining process. Typical Al-TiB master alloy micrograph at 100x magnification is clearly showing TiAl3 grain size distribution in aluminum matrix.No Image

ADVANTAGES OF AL-TIB FOR GRAIN REFINING :

Grain refininment of aluminum alloys provide number of technical and economical advantages.No Image

  • Imporoved feeding: fine grains promote an easier flow of the molten metal feeding the shrinkage during the final stages of solidification resulting in smaller and more uniform dispersed shrinkage porosity.
  • Reduced ingot cracking: fine grains provide a complex network of grain boundries, reducing the tendency of crack inititation and propogation. This results in the virtual elimination of centerline cracking in DC-cast ingots even at high casting speeds
  • Reduced porosity: as voids from internal shrinkage or dissoved gas are intergranular, fine grains inhibit the concentartion of porous zones to improve soundness of casting Better homogenity: with a fine as cast grain size, second phases and impurities accumualting along the grain boundries during solidification are finer and more uniformly distributed.
  • Improved mechanical properties: grain boundries are high energy areas along which fracture cracks can inititate and propogate easily. Small randonmly orientated grains minimize this tendency and provide improved ductility in the form of uniform and total elongation, reduction in area and fracture toughness. Furtehr in some cases grain refining can provide uniform directional properties and improved machinabilty.
  • Reduced costs: improvement which results from grain refinement of the cast products results in increased yields of products and reduced product cost

PRODUCT DESCRIPTION:

Al-TiB master alloy with different titanium to boron ratios from 3:1 to 5:0.2 are produced to accommodate needs of the users plant. Proper selection of grain refiner alloy, need consideration for chemisytry of alloy to be treated, the purity and portion of scrap or secondary aluminum used, the desired grain size in the product and melting / casting process used.

Minex produces Al-TiB in waffle, cast bar, cut rods and continous rods form. Minex’s rod products are manufactured through specialised unidirecional stirring induction furnace providing effective utilisation of power to alloy output ratio and imporved salt recoveries with controlled and uniform grain stractures in aluminm matrix, followed by proprietory process. The grain refiner rods are suitable for continuous additions through launder for continous casting opertaions. The performance of the rod products are illustrated in the adjacent photographs .

COMPOSITION OF ALLOY:

ALLOY COMPOSITION APPLICATION
AL-TIB 5/1 Ti: 4.5-5.5, B: 0.8-1.2 Si: 0.20, Fe: 0.30, V: 0.02 Highly efficient and versatile refiner for wide range of castings
AL-TIB 5/0.2 Ti: 4.5-5.5, B: 0.15-0.25 Si: 0.20, Fe: 0.30, V: 0.02 Powerful grain refiner for boride sensitive applications as foils, canstock and surface critical profiles
AL-TIB 3/1 Ti: 2.5-3.5, B: 0.8-1.2 Si: 0.20, Fe: 0.30, V: 0.02 An efficient and cost effective refiner for many applications
FORMS ALLOYS COILED ROD 9.5MM CUT ROD 9.5MM CAST BAR WAFFLE INGOT
AL-TIB 5/1 YES YES YES YES
AL-TIB 5/0.2 YES YES YES YES
AL-TIB 3/1 YES     YES

9.5 mm diameter rod in stanadard 180 kgs coils. These are developed for addition into the metal transfer lunder in continous or semi continous casting operations enabling continous grain refining within 1-2 mintues of addition. Due to its propeties rod is suited for start-stop semi contonous addition in automated castings lines.

9.5 mm diamter rod cut into 50cm (100 gms) or 100 cm (200 gms) pieces. Ideally suitaed for foundries to make accurate grain refiner additions to ladle and crucibles. Combining easy handling with superior metallurgical peroducts. Exact additions are made by simply stirring the required number of rods into the melt.

For furnace additions Al-TiB as castbar or waffle ingot is added as the melt treatment is completed, usually within 20 mintues prior to casting ensuring reliable grain refinement of ingots.