Aluminum alloys for hobby foundry


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Aluminum alloys for hobby foundry

  1. 1. 1<br />Aluminum Foundry Alloy Basicsfor Foundry JoeRev 0, May 2010<br />
  2. 2. 2<br />Content<br />Basics of Aluminum Alloys<br />Cast vs. Wrought<br />Primary vs. Secondary<br />Understand Alloy Element Effects<br />Deliberate Additions<br />Si, Mg, Cu, Zn, Be<br />Unwanted Additions<br />Fe, Others<br />Effects of Gases (H2, O2)<br />Grain Refiners (TiBor)<br />Modifiers (Sr)<br />
  3. 3. 3<br />Aluminum Alloy Applications<br />
  4. 4. 4<br />Basics of Aluminum Alloys<br />Wrought alloys <br />Wrought means “worked”<br />Rolled, Extruded, Forged<br />6061, 7075 Aircraft Aluminum<br />3104 Beer cans<br />Casting alloys are different than wrought<br />Have been specifically designed <br />to be cast and not worked<br />
  5. 5. 5<br />Aluminum Foundry Casting Alloys<br />In North America the Aluminum Association numbering system is most common<br />Wrought alloys series have 4 numbers<br />1000 to 9000 series<br />6061, 7075 are familiar examples<br />Foundry alloy series have 3 numbers<br />100 series to 800 series<br />319, 356, 380 are the most common foundry alloys<br />There are more than 60 foundry alloys<br />But just a few make up 80% of tonnage cast<br />
  6. 6. 6<br />Wrought vs. Cast Aluminum<br />
  7. 7. 7<br />Primary vs. Secondary Alloys<br />Primary Alloy<br />Produced from ore at a smelter<br />Virgin ingot – first time used<br />More expensive<br />Secondary Alloy<br />Produced from scrap by a recycler<br />Lower cost<br />Does NOT mean low quality!<br />
  8. 8. 8<br />Some Foundry Alloy Examples<br />Foundry Alloys are mostly aluminum <br />with 2 or 3 deliberate additions of alloying elements to improve properties<br />They also have some unwanted elements <br />which usually reduce properties<br />
  9. 9. 9<br />What do all these Alloying Elements Do?<br />Deliberate Alloy Additions<br />Si, Mg, Cu, Zn<br />Unwanted Alloy Additions<br />Fe, Many Others<br />Other Additives<br />Grain Refiners (TiBor)<br />Modifiers (Sr)<br />Effects of Gases (H2, O2)<br />
  10. 10. 10<br />Deliberate Alloy Additions<br />These alloy elements are added by design<br />Added on purpose, to create some kind of a benefit<br />The “Big One” is Silicon<br />Develops a property called “fluidity”<br />Next biggest is Magnesium<br />Allows the alloy to respond to heat treat for improved strength<br />
  11. 11. What is Meant by Fluidity? <br />Fluidity is how far the alloy will flow before freezing<br />If the alloy freezes before it fills the mold you get a <br />short pour <br />misrun, or <br />cold shut<br />You could just make the metal hotter (superheat) so it will run more before freezing<br />But that takes energy and costs money<br />This pattern is poured to measure fluidity <br />11<br />
  12. 12. How to Improve Fluidity? <br />Instead of making the metal hotter <br />we can alloy the Aluminum to lower the melting point, so<br />the alloy will run farther for a given temperature<br />An eutectic alloy has this property<br />This is best seen on a phase diagram<br />A Degree in Metallurgy follows on the next 3 slides<br />12<br />
  13. 13. 13<br />Solder Phase Diagram<br />Solder is an Eutectic Alloy<br /> mean lowest melting point<br />Pure Tin melts at 446°F 230°C<br />Pure Lead melts at 626°F 330°C<br />BUT!<br />A 60/40 mix melts at 338°F 170°C<br />One hundred degrees F cooler!<br />Less energy required to melt!<br />Solid<br />
  14. 14. 14<br />Aluminum Silicon Phase Diagram<br />Aluminum Silicon is also an Eutectic Alloy<br />Pure Aluminum melts at 1220°F 660°C<br />Pure Silicon melts at 2552°F 1400°C<br />BUT!<br />An 11.7% mix melts at 1070°F 577°C<br />One hundred fifty degrees F cooler!<br />Less energy required to melt!<br />LIQUID<br />SLUSH<br />SOLID<br />Pouring temp is temp above melt point required to fill thinnest section before freezing<br />So by using a eutectic alloy, can reduce the pouring temp<br />
  15. 15. 15<br />Silicon Content of Foundry Alloys<br />319 alloy<br />engine blocks heads, intakes<br />LIQUID<br />390 alloy<br />Vega engine block<br />380 alloy<br />transmission cases<br />SLUSH<br />SLUSH<br />413 eutectic alloy<br />“perfect” foundry alloy - lowest shrink<br />SOLID<br />
  16. 16. Review of Element Effects<br />16<br />
  17. 17. 17<br />Base Element – Aluminum (Al)<br />100 Series Alloys are mostly Aluminum<br />13th element on Periodic Table<br />Aluminum has limited use in pure form <br />Electrical wire, electric motor rotors<br />Very tricky to cast<br />Usually mixed with other elements<br />Mix of elements is “an Alloy”<br />
  18. 18. 18<br />Effects Of Alloy Elements – Silicon (Si)<br />300 & 400 Series Alloys have Silicon added<br />SiO2 is quartz <sand – used to make glass> <br />Added to improve castability<br />increases fluidity, reduces shrinkage<br />Silicon and Magnesium together<br />makes alloy heat treatable for strength<br />356 and 413 alloys are high Silicon alloys<br />Nice to cast<br />
  19. 19. 19<br />Effects Of Alloy Elements – Copper (Cu)<br />200 Series Alloys have Copper added<br />Copper increases strength<br />Reduces corrosion resistance<br />Increases shrinkage <br />makes alloy more difficult to cast<br />
  20. 20. 20<br />Effects Of Alloy Elements – Magnesium (Mg)<br />300 & 500 Series Alloys have Magnesium added<br />Silicon and Magnesium together<br />makes alloy heat treatable for strength<br />Increases shrinkage <br />makes alloy more difficult to cast<br />
  21. 21. 21<br />Effects Of Alloy Elements – Zinc (Zn)<br />700 Series Alloys have Zinc added<br />Zinc and Aluminum <br />has bright surface finish<br />good corrosion resistance <br />good strength<br />Increases shrinkage <br />makes alloy more difficult to cast<br />
  22. 22. 22<br />Unwanted Alloy Additions - Tramps<br />These alloy elements are not wanted<br />Can’t be helped<br />From smelting process<br />From scrap recycling<br />From contact with iron crucibles, tools<br />They cause some kind of harm<br />Lower strength<br />Worse castability<br />Tramp Elements<br />
  23. 23. 23<br />Effects Of Alloy Elements – Iron (Fe)<br />Iron Oxide is rust <br />Iron makes an Alloy more brittle<br />Generally regarded as bad<br />Try to keep as low as possible<br />Aluminum is an aggressive solvent for iron<br />Steel crucibles & tools dissolve in Aluminum<br />Use a coating<br />
  24. 24. 24<br />Alloy Microstructure<br />Aluminium is soft and ductile<br />Silicon is hard and brittle<br />Both = stronger<br />Think Fiberglas Glass & Resin<br />Si<br />Brittle<br />Dark<br />Color<br />Al<br />Soft<br />Light Color<br />
  25. 25. 25<br />Iron in Microstructure<br />Si<br />Brittle<br />Al<br />Soft<br />(Fe,Mn)3Si2Al15<br />Chinese Script (-Fe)<br />FeSiAl5<br />Needles (-Fe)<br />A crack along the brittle Iron phase<br />
  26. 26. 26<br />Other Minor Tramp Elements<br /><ul><li>Chromium, Nickel, Tin
  27. 27. Lithium, Calcium, Phosphorous
  28. 28. Others
  29. 29. Each and Total
  30. 30. Just control them under the spec limit
  31. 31. How?
  32. 32. Add more Aluminum to dilute them down</li></li></ul><li>27<br />Effects of Gases on Alloys<br />Gases also have a major <bad> effect on Aluminum alloys<br />Hydrogen<br />Oxygen<br />
  33. 33. 28<br />Effect of Hydrogen Gas - Porosity<br /><ul><li>Causes “Gas” Porosity
  34. 34. Pores reduce strength, ductility
  35. 35. Cause leakers
  36. 36. Cause machining scrap
  37. 37. Control by “de gassing”
  38. 38. Chlorine tablets
  39. 39. Inert gas bubbling
  40. 40. Rotary impeller degasser</li></li></ul><li>29<br />Effect of Oxygen Gas - Dross<br />Aluminum oxidizes immediately<br />Skim your melt and watch it grow<br />Oxides reduce strength<br />Think crumpled ball of “tin” foil<br />Control by cleaning with salt fluxes<br />
  41. 41. 30<br />Aluminum Grain Refiners - TiBor<br />Create a fine, uniform as-cast grain structure <br />Finer grains increase strength<br />Reduces cracking<br />Combats shrinkage porosity<br />Grain Refined<br />Not Grain Refined<br />
  42. 42. 31<br />Modifiers (Strontium)<br />Changes the structure of the AlSi phase from “needle like” to “globular” <br />Combats shrinkage porosity <br />Improves strength<br />Increases ductility<br />Sodium was the original modifier<br />but has mostly been replaced by Strontium<br />less reactive when added to the melt<br />
  43. 43. 32<br />Modifiers (Strontium)<br />Modification of the Silicon phase<br />From long brittle needles to small globules<br />Si<br />Brittle<br />Al<br />Soft<br />Unmodified<br />Modified<br />