4. 4 Basics of Aluminum Alloys Wrought alloys Wrought means “worked” Rolled, Extruded, Forged 6061, 7075 Aircraft Aluminum 3104 Beer cans Casting alloys are different than wrought Have been specifically designed to be cast and not worked
5. 5 Aluminum Foundry Casting Alloys In North America the Aluminum Association numbering system is most common Wrought alloys series have 4 numbers 1000 to 9000 series 6061, 7075 are familiar examples Foundry alloy series have 3 numbers 100 series to 800 series 319, 356, 380 are the most common foundry alloys There are more than 60 foundry alloys But just a few make up 80% of tonnage cast
7. 7 Primary vs. Secondary Alloys Primary Alloy Produced from ore at a smelter Virgin ingot – first time used More expensive Secondary Alloy Produced from scrap by a recycler Lower cost Does NOT mean low quality!
8. 8 Some Foundry Alloy Examples Foundry Alloys are mostly aluminum with 2 or 3 deliberate additions of alloying elements to improve properties They also have some unwanted elements which usually reduce properties
9. 9 What do all these Alloying Elements Do? Deliberate Alloy Additions Si, Mg, Cu, Zn Unwanted Alloy Additions Fe, Many Others Other Additives Grain Refiners (TiBor) Modifiers (Sr) Effects of Gases (H2, O2)
10. 10 Deliberate Alloy Additions These alloy elements are added by design Added on purpose, to create some kind of a benefit The “Big One” is Silicon Develops a property called “fluidity” Next biggest is Magnesium Allows the alloy to respond to heat treat for improved strength
11. What is Meant by Fluidity? Fluidity is how far the alloy will flow before freezing If the alloy freezes before it fills the mold you get a short pour misrun, or cold shut You could just make the metal hotter (superheat) so it will run more before freezing But that takes energy and costs money This pattern is poured to measure fluidity 11
12. How to Improve Fluidity? Instead of making the metal hotter we can alloy the Aluminum to lower the melting point, so the alloy will run farther for a given temperature An eutectic alloy has this property This is best seen on a phase diagram A Degree in Metallurgy follows on the next 3 slides 12
13. 13 Solder Phase Diagram Solder is an Eutectic Alloy mean lowest melting point Pure Tin melts at 446°F 230°C Pure Lead melts at 626°F 330°C BUT! A 60/40 mix melts at 338°F 170°C One hundred degrees F cooler! Less energy required to melt! Solid
14. 14 Aluminum Silicon Phase Diagram Aluminum Silicon is also an Eutectic Alloy Pure Aluminum melts at 1220°F 660°C Pure Silicon melts at 2552°F 1400°C BUT! An 11.7% mix melts at 1070°F 577°C One hundred fifty degrees F cooler! Less energy required to melt! LIQUID SLUSH SOLID Pouring temp is temp above melt point required to fill thinnest section before freezing So by using a eutectic alloy, can reduce the pouring temp
17. 17 Base Element – Aluminum (Al) 100 Series Alloys are mostly Aluminum 13th element on Periodic Table Aluminum has limited use in pure form Electrical wire, electric motor rotors Very tricky to cast Usually mixed with other elements Mix of elements is “an Alloy”
18. 18 Effects Of Alloy Elements – Silicon (Si) 300 & 400 Series Alloys have Silicon added SiO2 is quartz <sand – used to make glass> Added to improve castability increases fluidity, reduces shrinkage Silicon and Magnesium together makes alloy heat treatable for strength 356 and 413 alloys are high Silicon alloys Nice to cast
19. 19 Effects Of Alloy Elements – Copper (Cu) 200 Series Alloys have Copper added Copper increases strength Reduces corrosion resistance Increases shrinkage makes alloy more difficult to cast
20. 20 Effects Of Alloy Elements – Magnesium (Mg) 300 & 500 Series Alloys have Magnesium added Silicon and Magnesium together makes alloy heat treatable for strength Increases shrinkage makes alloy more difficult to cast
21. 21 Effects Of Alloy Elements – Zinc (Zn) 700 Series Alloys have Zinc added Zinc and Aluminum has bright surface finish good corrosion resistance good strength Increases shrinkage makes alloy more difficult to cast
22. 22 Unwanted Alloy Additions - Tramps These alloy elements are not wanted Can’t be helped From smelting process From scrap recycling From contact with iron crucibles, tools They cause some kind of harm Lower strength Worse castability Tramp Elements
23. 23 Effects Of Alloy Elements – Iron (Fe) Iron Oxide is rust Iron makes an Alloy more brittle Generally regarded as bad Try to keep as low as possible Aluminum is an aggressive solvent for iron Steel crucibles & tools dissolve in Aluminum Use a coating
24. 24 Alloy Microstructure Aluminium is soft and ductile Silicon is hard and brittle Both = stronger Think Fiberglas Glass & Resin Si Brittle Dark Color Al Soft Light Color
25. 25 Iron in Microstructure Si Brittle Al Soft (Fe,Mn)3Si2Al15 Chinese Script (-Fe) FeSiAl5 Needles (-Fe) A crack along the brittle Iron phase
41. 30 Aluminum Grain Refiners - TiBor Create a fine, uniform as-cast grain structure Finer grains increase strength Reduces cracking Combats shrinkage porosity Grain Refined Not Grain Refined
42. 31 Modifiers (Strontium) Changes the structure of the AlSi phase from “needle like” to “globular” Combats shrinkage porosity Improves strength Increases ductility Sodium was the original modifier but has mostly been replaced by Strontium less reactive when added to the melt
43. 32 Modifiers (Strontium) Modification of the Silicon phase From long brittle needles to small globules Si Brittle Al Soft Unmodified Modified
