Alloying in the Cast House

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Alloying in the Cast HouseMQW5 March 2012 2

Alloying in the Cast HouseMQW5 March 2012 3

Factors in Choice of Alloying MethodDissolution RateElement YieldsCONSISTENCY& COSTare the key factorsEase of AdditionHES/EmissionsImpurities & CleanlinessMQW5 March 2012 4

Alternative Methods of AlloyingHighPure MetalsSi, Mg, Zn, Cu (Fe)Powder InjectionMn, (Fe, Cr)Tablets/BriquettesMn, Fe, Cr, Ti, (Cu, Ni)LowCostHigh ConcentrationMaster AlloysMn splatter, SiDilute Master AlloysB, Zr, Ti, V, Sr (Mn, Cr etc)HighMQW5 March 2012 5

% RecoveryDissolution Rates of Mn Additives10090807060504030201000 5 10 15 20 25 30Dissolution Time (minutes)MnFlake Mn20 Wafle Mn80ZF Mn80Flux Mn60 SplatterMQW5 March 2012 6

Metal CleanlinessReference work on Prefil ® and PoDFA from Ohm and Bauer, TMS 2008HighMn FlakeMn80Zero FluxMn80FluxMn60SplatterMn20WaffleLow Cleanliness HighMQW5 March 2012 7

Alloying in the Cast HouseIntroduction to AlloyingMechanisms of DissolutionComparison of Tablet TypesConclusionsMQW5 March 2012 8

Mechanisms of Dissolution (simplified version!)• The binding agent melts or dissolves to expose the element powder• The metallic element in powder form does not ‘dissolve’ – it formscomplex intermetallics• These intermetallics then dissolve in the liquid aluminium• The process is diffusion controlled and hence dependent upon:– Alloy type; temperature; degree of stirring; concentrationNo stirIncubationIntermetallicsTimeWith stirMQW5 March 2012 9

Photomicrographs of Tablet DissolutionMn particle dissolvingAlloyed meltMnMn aluminidephasesMQW5 March 2012 10

Tablet DissolutionSwelled CompactsMn75% - 730ºC0’’ 30’’ 45’’ 60’’ 70’’seconds after additionMQW5 March 2012 11

Alloying in the Cast HouseIntroduction to AlloyingMechanisms of DissolutionComparison of Tablet TypesConclusionsMQW5 March 2012 12

Types of Alloying TabletsComposition75%, 80%, 85%, 100%PackagingFoil wrap, plastic wrap,20kg paper sacks, big bagsElementsMn, Fe, Cr, Cu, TiBinderFlux, Al powderSize100gm, 200gm, 1000gmMQW5 March 2012 13

% RecoveryTablet Compositions (75 – 100%)• Higher contents give lower unit cost but slower dissolution rates• Optimum product depends on specific cast house operation• In general 80% content will work in most cast houses100Comparison of Mn Additives90807060504030201000 5 10 15 20 25 30Dissolution Time (minutes)MnFlake Mn75ZF Mn80ZF Mn85ZFMQW5 March 2012 14

Alternative Types of Binder• Aluminium powderI. Primary or secondaryII. Aluminium reacts with elements to form intermetallics whicheventually ‘burst’ the compact and then dissolve• FluxI. Normally potassium aluminium fluorideII. Flux dissolves oxide layers on powder to reduce dissolutiontimeIII. Flux melts and releases individual particles into meltIV. Can also be used in conjunction with aluminium powder• Organic binderI. Sometimes used in briquettes with aluminium powderII. Gives high reaction on addition to melt which aids fastdissolutionMQW5 March 2012 15

Flux or No Flux Tablets?Benefits of Flux Tablets• Lower cost• Faster dissolution• Can help in removing oxides from the meltPotential Disadvantages of Flux Tablets• Fume generation• Potential refractory erosion and reaction with distribution bags• Potential for liquid flux remaining in liquid aluminium at high additions that canadversely effect end quality• Excess flux will reduce the Al content of the dross – offset by increasing the Almetal yield in the furnace?General Recommendation• Flux tablets are normally used for TRIM Additions.• Gives benefits of faster dissolution, lower cost and the low levels do not giveexcessive fumes or refractory erosion• When larger additions are made, requires a careful study of overall flux/fluorideinput to the melt to avoid adverse effectsMQW5 March 2012 16

• Packaging– Foil, plastic, paper bags– In ~20kg cardboard cartons / paper bags or 1,000kg big bags• Tablet sizePackaging and Size of Tablets– Mini or large tablets 100gram, 200grams, 1000kgs• In general packaging types and tablet size does NOT affectdissolution rates or yield• Choice of packaging is related to individual cast house choice• There is an interest to evaluate bulk additions to minimise manualhandling in the cast houseMQW5 March 2012 17

Good Cast House Practice• Add tablets to clean melt surface at 720 – 750 O c• Distribute evenly over melt surface, not in one area• Stir bottom of furnace well for 5-10 minutes• Be aware of “cold spots” when adding several elements together• AVOID:-DrossFinesOxidation [Mg, Sr …]IntermetallicsHeavyelementsMQW5 March 2012 18

Conclusions• There is a very wide choice of alloying additivesavailable in the market• The optimum alloying method is very cast housespecific• A detailed process evaluation is needed tooptimise choice of alloying product and casthouse process• With good practice, cast houses cansignificantly reduce the total cost of alloyingMQW5 March 2012 19

Contact details:-Dan StephensonRegional Sales ManagerLondon & Scandinavian Metallurgical Co LimitedFullerton RoadRotherhamS60 1DLEnglandTel: +44 (0)1709 828 500Email: dstephenson@lsm.co.ukMQW5 March 2012 20