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KB Alloys, Inc. has been a leadingproducer of aluminum-based masteralloys since its inception as KaweckiChemical Company during 1950.KB Alloys manufactures a full line ofmaster alloys, grain refiners, modifiersand hardeners to meet the metaltreatment and alloying requirementsof the aluminum cast metals industry.
From strategically located manufacturing and warehousing facilities inthe USA, Europe and Asia, KB Alloysdelivers consistently dependable products anywhere in the world.
To further serve the aluminum andnon-ferrous foundry industry, KB Alloys'staff of technical specialists andexperienced field sales engineersare available for technical assistance.They are supported by KB AlloysMetallurgical Services and TechnologyDepartments.
Aluminum..BaseMaster AlloysToday's foundryman realizes that closecontrol of the as-cast structure and chemicalcomposition of the alloy are major requirements in the production of quality castings.Three types of master alloys are essential tothe foundryman: grain refiners, modifiers,and hardeners.
When grain refiners were first used inaluminum casting alloys, they were addedas titanium and boron salts to the moltenalloy in the furnace. Alloying elements wereusually added in the form of pure metals.By present day standards, such practicesare generally inefficient and enVironmentallyunacceptable.
Development of aluminum-base masteralloys in 1955, by Kawecki ChemicalCompany, a predecessor of KB Alloys, madeit possible to add the required elementsfaster, more economically and above all,more uniformly than was previously possible.KB Alloys produces a full line of aluminumbase master alloys which are convenientto use and provide the desired elementaladdition. This assures uniformity and predictability of the required alloy composition.These I master alloys are available in avariety of forms: waffle ingot, slab, button,bar, coiled and cut rod.
A356 alloy as-cast structure. (2X)
TIBOR® Grain RefinersIn aluminum castings, a large dendritic grainstructure is generally undesirable. The mosteffective way to provide a fine and uniformas-cast grain structure is to add nucleatingagents to the melt to enhance crystalformation during solidification. KB AlloysTIBORilD family of aluminum master alloyscontaining titanium and boron providea convenient means of introducing highlyeffective nucleating agents.
Grain refinement of aluminum alloysprovides a number of technical andeconomic advantages.
Reduced Hot Tearing: Fine equiaxed grainsprovide a uniform network of grain boundaries, and reduce the tendency for crackinitiation and propagation. In foundrycastings, this structure reduces the tendencyfor "hot tearing" and "hot cracking" duringsolidification.
Improved Feeding: Fine grains promotean easier flow of the molten metal that feedsthe shrinkage during the final stages ofsolidification, and result in smaller and moreuniformly dispersed shrinkage porosity.
Reduced Porosity: Voids from internalshrinkage or dissolved gas are intergranular;with fine grains these voids are smallerand more uniformly distributed at the grainboundaries, thus improving the soundnessof the casting.
Better Homogeneity: Secondary phasesand impurities that accumulate along grainboundaries during solidification are also finerand more uniformly dispersed.
Improved Mechanical Properties: Grainboundaries are high energy areas alongwhich fracture cracks can initiate andpropagate easily. Small closely knit grainsminimize this tendency and provide highermechanical properties.
Improved Surface Finish: A fine grainstructure improves the surface finish of acasting, especially when the piece is brightdipped or anodized.
Reduced Cost: The improvements whichresult from grain refinement of the castingsincrease the product yield and reduceproduct costs.
A356 alloy grain refined as-cast structure. (2X)
Figure 1
- . .TIBOR@
1Figure 3. Grain refining response of 5%Ti-1.0%B when added to A356 alloycontaining residual titanium and strontium. Case A ~ 0.005% Ti and no Sr. CaseB =0.005% residual TI and 0.015% Sr. Case C ~ 0.15% residual Ti and no Sr.Case D ~ 0.15% residual Ti and 0.015% Sr. Grain refiner addition is 2 Ibs per1,000 ibs A356 alloy in all cases.
0.15
o
o
1.711.4
C
c
Figure 2(a)
Figure 2(b)
B
5.011.0
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A
In today's practice, Aluminum-StrontiumMaster Alloys provide a reliable methodfor adding strontium to molten aluminum.Recovery is high, and loss during holding is reduced significantly compared tosodium, even to the extent that aluminumingot preViously modified with strontiumcan be remelted with good retention ofstrontium. This led to the development of"permanently modified" aluminum siliconalloys.
Strontium ModificationThe search for alternative-elementsfor modifying aluminum silicon alloysrevealed that strontium master alloycould be used in place of sodium.Fortunately, none of the special precautions required in the use and handlingof sodium apply to the strontium masteralloy, and superior recovery and performance are achieved with strontium as amodifying agent.
450.--------------------.
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0.005Residual To (%)
Fogure 1. Grain refining response of 5% Tl-l.0%B and 1.7% Ti-1.4%B Whenadded 10 A356 alloy having low and high residual To levels. Grain refiner addilionis 2 100 per 1,000 100 A356 alloy In all cases.
1Ftgure 2. GraIn refining response of 1.7% TI-1.4%B when added 10 A356 alloycon1aining residual titanium and strontium. Case A ~ 0.005% Ti and no Sr. CaseB ~ 0.005% residual nand 0.015% Sr. Case C ~ 0.15% residual To and no Sr.Case 0 = 0.15% residual To and 0.015% Sr. Grain refiner addition is 2 Ibs per1,000 Ibs A356 alloy in all cases.
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I 350~iii 300c;
'ECJ 250
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The improvements in propertiesthat resulted were greatlyresponsible for the increase inuse of these alloys. However,sodium is a very reactivemetal. It can react when exposed to air and can burnviolently during addition tothe molten aluminum siliconalloy, therefore, close controland the level of additionsis difficult.
Modification produces a silicon phase that isfibrous and finely dispersed. Ductility of thecastings markedly improves, and thetendency for cracking or brittlefracture is less. For many years,sodium was the only meansavailable for the modification ofaluminum silicon alloys.
ModifiersA major portion of the aluminum alloys usedto produce castings in the foundry industrycontain silicon in the range of 5% to 12%.When unmodified melts of these alloysare used, coarse platelet crystals of thealuminum silicon eutectic phase form inthe casting during solidification. These particles are brittle and reduce the strength andductility of the casting by inhibiting flow ofmolten metal ("feeding") into areas of thecasting as it solidifies.
but does contain 0.15% residual Ti. Finally,Case D which represents the smallestgrain size obtained contained 0.15%residual Ti and 0.015% Sr. Clearly, whengrain refiner performance is evaluated on apound per pound basis, TIBORfI 5%Ti-1.0%B is the most powerful product foruse with Sr modified alloys such as A356.
After addition to moltenaluminum, sodium tends tovolatilize during holding ofthe melt, leading to furtherlosses. Excessive additions tocompensate for loss can leadto "over modification" with theformation of coarse AI-Si-Nacompounds and SUbsequentdeterioration in structureand mechanical properties.The need for a non-sodiummodifier was clear.
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Grain Refiner InteractionsIn the production of foundry alloy ingot, itis common practice for the ingot producerto add titanium to his alloy to enhance thealloy's response to later additions of TIBOR(!lgrain refiners. We commonly refer to thisas "residual titanium" and it is typicallypresent at levels ranging from -0.15 - 0:30%.In addition, aluminum-silicon foundry alloysare typically modified via additions ofstrontium, either by the ingot producer or bythe foundryman.
KB Alloys Technology Group has studiedthese factors and interactions relative·to theperformance of 5% Ti-1.0%B and 1.7%T-1.4%B TIBORfI. It was confirmed that bothproducts producer a smalle grain sizewhen added to an alloy containing residualtitanium as illustrated in Figure 2(a). In bothcases, the grain size was reduced from -415microns to -355 microns.
This work also investigated possibleinteractions between strontium and grainrefiners. In the presence of strontium,TIBOR® 5% Ti-1.0%B produces a smallergrain size than does TIBORfi 1.7%T-1.4%B.In fact, no interaction was observed betweenstrontium and TIBOR@ 1.7% Ti-1.4%B asdemonstrated in Figure 2(b). The resultshowever are different with 5%Ti-1 %B asillustrated in Figure 2(c). The largest grainsize is represented by Case A wherethere was no Sr addition and residual Tiwas at the low level of 0.005%. Case B isthe same as A, but includes a Sr additionof 0.015%. Case C received no Sr addition,
KB Alloys TIBOR(!l family of master alloygrain refiners are available in a range ofchemical compositions and titanium toboron ratios. However the most effective andmost commonly used grain refiners foraluminum casting alloys contain either5% Ti-1.0% B or 1.7% Ti-1.4%B. Bothproducts are available in button, waffleingot, bar, coiled and cut rod form.
Choice of TIBOR® Alloy forGrain RefinementKB Alloys produces TIBORfi in button,waffle ingot, bar, coiled and cut rod form.Product form and performance attributescan be tailored to fit customers productionpractices.
Beyond the differences in chemical composition, the intermetallic boron phasesdiffer significantly between the two products.In the 5%Ti-1%B composition, the boronintermetallic phase is present as TiB2particles. The 1.7%Ti-1.4%B compositionhas a "mixed boride" intermetallic phase.
Figure 2(c)
0 ••1 I~.l
Aluminum-StrontiumMaster AlloysKB Alloys produces and markets a varietyof aluminum master alloys containingstrontium.
A residual concentration of 0.01 % to0.02% strontium is usually adequate forfull modification of hypo-eutectic andeutectic alloys. However, excess additionsdo not cause over modification, althoughconcentrations greater than about 0.1 %should be avoided because detrimentalAISrSi intermetallics may start to form.Furnace practice, alloy composition, andsolidification rate of the casting will influenceoptimum level to be used in production.
Proper strontium additions to aluminumsilicon alloys improves as-cast mechanicalproperties. Improvements in elongationfrom 50% up to 200% can be achieved.Increases in ultimate tensile strength of 20%,have been reported as well as improvedsurface texture and machinability performance of the castings.
There is evidence that strontium promotesthe formation of finer particles of iron-richintermetallic compounds instead of therelatively large particles of more brittle ironaluminum-silicon phase. These fine particlesincrease the ductility of aluminum siliconcasting alloys with high iron content.
As shown in Figure 2(c) strontium additionspromote a positive interaction with titaniumand boron. Together strontium and TIBOR~
interact to further refine grain structurethan TIBO alone. KB Alloys TIBORproducts are an ideal family of grainrefiners for use in both modified andunmodified alloys.
Summary1. KB Alloys strontium aluminum master
alloys provide reliable, effective meansof adding strontium to modifyaluminum alloys.
. 2. Castings made from melts properlymodified with strontium are more soundand have significantly improvedmechanical properties, particularlyductility, than castings made withunmodified melts.
3. Strontium is a more cost effectivemodifier than sodium for aluminumsilicon hypoeutectic casting alloys.Under controlled conditions, strontiummodified ingots can be remelted andretain the modified structure.
4. The use of aluminum strontiummaster alloys avoids the need for thespecial precautions associated withuse of metallic sodium.
5. Strontium tends to reduce the size ofthe iron-rich compounds, if present,resulting in improved ductility ofiron-containing aluminum siliconcasting alloys.
6. Strontium modified ingot and sodiummodified ingot may be melted and mixedtogether without loss of modification. Ifthe modification melt mixture requiresal;lditional modification, more strontiummay be added to obtain the desiredstructure.
7. Additions of sodium as a metal to amelt of strontium modified ingot arenot recommended because of the
Strontium modified, as-caststructure of A356 alloy.Note finely dispersed fibrousstructure of silicon phase. (400X)
possibility of "over modification", i.e.,formation of undesirable AL-Si-Nacompounds.
8. Degassing of a strontium modifiedmelt should be performed_ with drynitrogen or argon gas.
9. The use of salts for grain refining orfluxing should be avoided becausechlorine and flourine will removestrontium from the melt.
10. Phosphorous, even in small amountsshould be avoided because it will 'poison the ability of strontium tomodify the silicon phase.
11. When grain refiner performance isevaluated on a pound for pound basis,TIBOR- 5%Ti-1 %B is the most powerfuland effective grain refining product foruse with strontium modified alloys suchas A356.
Unmodified, as-cast structure ofA356 alloy. Note the coarseplatelet crystals of siliconeutectic phase. (400X)
Figure 3
AluQ'linum Hardener AlloysAlloying elements are added to aluminumto improve the mechanical and physicalproperties of the final product. In orderto overcome the disadvantages of adding pure elemental metals to the meltingfurnace, aluminum-base master alloys weredeveloped that are rich in one or more of thedesired addition elements. This family ofmaster alloys, frequently referred to ashardeners, is used to add alloying elementsto aluminum to produce alloys with improvedstrength, hardness, fracture toughnessand corrosion resistance. Master alloys ofcopper, magnesium, manganese, bismuthand chrome are examples.
68% MgKB Alloys introduced a new formulation toits magnesium aluminum hardeners line ofalloys. By raising the concentration ofmagnesium from the traditional 25% and 50%levels to that of 68%, the new formulationtakes advantage of the traditional benefitsassociated with the use of a master alloy,while the higher composition rivals theeconomics of alloying with pure magnesiumthrough the benefits of better recoveries,improved through-put with lower meltingpoints and cleaner melts.
The new product is exclusiv~ to KB Alloysand comes in a variety of sizes and forms tosuit the needs of a wide range of customerapplications. The 3.5 ounce button isdesigned for small furnace alloying or"touch-up" for larger additions. The waffleand slab ingots provide a convenie'nt alloyingmethod for medium to large furnaceadditions. All shapes are producedunder an ISO registered process to insureconsistent chemical composition, ingotweight control and metallurgical cleanliness.
The 68% Mg product is design~d to benefitthe experienced alloyer. Because the densityis greater than that of pure magnesium(2.0g/cc vs. 1.7g/cc) the 68% Mg-AIalloy has less tendency to float and burn-off.Less burn-off means fewer oxides, betterrecoveries and cleaner melts. With its lowmelting temperature (43rC vs 650°C) the68% Mg alloy melts ultra-fast to keepproduction lines moving.
Modification Rating System forHypoeutectic Aluminum SiliconAlloysThe structure of an aluminum casting varieswith different casting parameters and mustbe controlled in order to provide consistentcastings. To achieve optimum properties, itis necessary to modify the morphology ofthe eutectic phase in hypoeutectic aluminumsilicon casting alloys. The cast structure ofhundreds of aluminum silicon alloy sampleshave been examined to establish the degree ofmodification. (1) Extensive experience withAluminum Association Alloy A356, whichcontains 6.5-7.5% silicon and 0.20-0.45%magnesium, has led to the formulation ofthe silicon phase modification rating systemshown in Figure 4.
1. D. Apefian. G. K. Sigworth and K. R. Whaler: "Assessment ofGrain Refining and Modification of AISi Foundry Alloys by ThermalAnalysis", AFS 7{ansactions. pp. 297-307 (1984).
Sample PreparationA small section is cut from the casting to beexamined, then polished on successivelyfiner grits of SiC sandpaper until a smoothand flat surface is obtained. The sample canthen be polished on cloth wheelsusing "A" and "B" grade aluminum oxidepowders until a mirror-like shine isobserved. The silicon phase can clearly beseen at 200x on the as-polished surface; abrief etch in a 5-10% HF solution will darkenthe silicon phase to make viewing easier.
Master Alloys
Sample EvaluationThe polished sample is examined at(200X) magnification.
The microstructures observed can beplaced in one of six overall classes.These are listed on Figure 4 with anumerical scale of Type 1 throughType 6 along with a descriptionof the structure. Photomicrographsof each type of structure at 200X arepresented for use as standardsrepresentative of each class.
It is now possible to assign any castingof hypoeutectic AI-Si alloy, a numericalvalue, which reflects its internalstructure to that of the rating systemshown in figure 4.
Modification Rating System (200x)
Type 1. Fully Unmodified Structure
Type 2. Lamellar Structure
Type 3. Partial Modification Structure
Figure 4
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Type 4. Non-Lamellar Structure
Type 5. Modified Structure
Type 6. Super Modified Structure
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FOUNDRYMEN'S GUIDE TO GRAIN REFINER ADDITIONS*SELECT CHARGE SIZE, CHOICE OF TIBOR·, PRODUCT FORM. READ QUANTITY REQUIRED.
TIBOR· 5%Ti /1 %B TIBOR·l.7%Ti /l.4%BNominal addition level: Nominal adClition level:
2 Ibstl,OOO Ibs (0.01 %Ti) 2 Ibst1 ,000 Ibs (0.01 %TO.907 kg/454 kg (0.01 %Ti) .907 kg/454 kg (0.01 %Ti)
5%TI/1%8 'CUT 'WAFFLE Kg WAFFLE 1.7%Ti/1.4%B 'CUT 'WAFFLECHARGE TIBO~ ROD "BUDON SECTION INGOT INGOT TIBO~ ROD "SUDON SECTIONGRAIN GRAINSIZE REFINER (1 oz) (50z) (1 Ib) (2.2Ibs) (16Ibs) REFINER (1 oz) (50z) (1 Ib)(Ibs or kg) REQUIRED (.03 kg) (.14 kg) (.454 kg) (1 kg) (7.25 kg) REQUIRED (.03 kg) (.14 kg) (.454 kg)
100lbs 0.21b 3 1 0.21b 3 145 kg .1 kg Rods Button .1 kg Rods Button
250lbs 0.51b 8 2 0.51b 8 2113 kg .23 kg Rods Buttons .23 kg Rods Buttons
500lbs 1 Ib 16 3 1 1 Ib 16 3 126 kg .454 kg Rods Buttons Section .454 kg Rods Buttons Section
1,0001bs 2 Ibs 7 2 1 21bs 7 2454 kg .907 kg Buttons Sections Ingol .907 kg Buttons Sections
1,5001bs 31bs 10 3 1 31bs 10 3680 kg 1.36 kg Buttons Sections Ingol+ 1.36 kg Buttons Sections
2,0001bs 4 Ibs 13 4 2 41bs 13 4908 k9 1.81 kg Buttons Sections Ingots 1.81 kg Buttons Sections
5,0001bs 10lbs 10 5 10lbs 102268 kg 4.54 kg Sections Ingots 4.54 kg Sections
10,0001bs 20lbs 20 9 1 20lbs 204540 kg 9.07 kg Sections Ingots Waffle+ 9.07 kg Sections
4Sections
,*Note: The addition levels shown are typical. Depending upon the casting method employed and the difficulty of the alloy, it may be necessary toincrease the addition level by a factor of 2 to 3x.
FOUNDRYMEN'S GUIDE TO STRONTIUM ADDITIONS*SELECT CHARGE SIZE& CHOICE OF STRONTIUM MASTER ALLOY. READ QUANTITY REQUIRED.
rI
STRONTIUM MASTER ALLOY 1O%Sr / AINominal addition level:,
1.5 Ibst1 ,000 Ibs (0.15% Sr) .68 kg/454 kg (0.15%Sr)
CHARGESTRONTIUM CUT WAFFLE WAFFLE
MASTER ROD SUDON SECTION SECTIONSIZE
ALLO~ (1 oz) (80z) (1 Ib) (16Ibs)'(Ibs or kg) REOUIR (.03 kg) (.23 kg) (.454 kg) (7.25 kg)
100lbs 0.151b 345 kg .07 kg Rods
250lbs 0.381b 6 1113 kg .17 kg Rods Button
500lbs 0.751b 12 2 126 kg .34 kg Rods Buttons Section
1,0001bs 1.51b 24 3 2454 kg .68 kg Rods Buttons Sections
1,5001bs 2.251bs 5680 kg 1.02 kg Buttons
2,0001bs 3 Ibs 6 3908 kg 1.36 kg Buttons Sections
5,0001bs 7.51bs 15 82268 kg 3.4 kg Suttons Sections
10,0001bs 151bs 15 14540 kg 6.8 kg Sections Waffle
*Note: The addition levels shown are typical. Depending upon the casting method employed and the difficulty of the alloy, it may be necessary toincrease the addition level by a factor of 2 to 3x.
