Aluminum alloys for hobby foundry
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Aluminum alloys for hobby foundry Aluminum alloys for hobby foundry Presentation Transcript

  • 1
    Aluminum Foundry Alloy Basicsfor BackyardMetalcasting.com Foundry JoeRev 0, May 2010
  • 2
    Content
    Basics of Aluminum Alloys
    Cast vs. Wrought
    Primary vs. Secondary
    Understand Alloy Element Effects
    Deliberate Additions
    Si, Mg, Cu, Zn, Be
    Unwanted Additions
    Fe, Others
    Effects of Gases (H2, O2)
    Grain Refiners (TiBor)
    Modifiers (Sr)
  • 3
    Aluminum Alloy Applications
  • 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
    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
  • 6
    Wrought vs. Cast Aluminum
  • 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
    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
    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
    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
  • 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
  • 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
    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
    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
  • 15
    Silicon Content of Foundry Alloys
    319 alloy
    engine blocks heads, intakes
    LIQUID
    390 alloy
    Vega engine block
    380 alloy
    transmission cases
    SLUSH
    SLUSH
    413 eutectic alloy
    “perfect” foundry alloy - lowest shrink
    SOLID
  • Review of Element Effects
    16
  • 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
    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
    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
    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
    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
    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
    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
    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
    Iron in Microstructure
    Si
    Brittle
    Al
    Soft
    (Fe,Mn)3Si2Al15
    Chinese Script (-Fe)
    FeSiAl5
    Needles (-Fe)
    A crack along the brittle Iron phase
  • 26
    Other Minor Tramp Elements
    • Chromium, Nickel, Tin
    • Lithium, Calcium, Phosphorous
    • Others
    • Each and Total
    • Just control them under the spec limit
    • How?
    • Add more Aluminum to dilute them down
  • 27
    Effects of Gases on Alloys
    Gases also have a major <bad> effect on Aluminum alloys
    Hydrogen
    Oxygen
  • 28
    Effect of Hydrogen Gas - Porosity
    • Causes “Gas” Porosity
    • Pores reduce strength, ductility
    • Cause leakers
    • Cause machining scrap
    • Control by “de gassing”
    • Chlorine tablets
    • Inert gas bubbling
    • Rotary impeller degasser
  • 29
    Effect of Oxygen Gas - Dross
    Aluminum oxidizes immediately
    Skim your melt and watch it grow
    Oxides reduce strength
    Think crumpled ball of “tin” foil
    Control by cleaning with salt fluxes
  • 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
  • 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
  • 32
    Modifiers (Strontium)
    Modification of the Silicon phase
    From long brittle needles to small globules
    Si
    Brittle
    Al
    Soft
    Unmodified
    Modified