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Solution time for A356 to T6

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  • Solution time for A356 to T6

    A friend and I are trying our hands at foundry work.

    We are using A356 and have gotten some good castings of a finned cylinder head for an air-cooled Kawasaki 2T triple. We want to heat treat them to T6 before machining.

    The ASM says solution time and temp is

    Solution 995-1005F time at temp 12 hours (from time at min temp) cool in water at 150-212F. T6 305-315F 2-5 hours
    From Mil-h-6088G:

    A356 solution HT @980-1025F when the max/min range exceeds 20F, and 20F temp range within the entire range may be utilized. HT above 1010F may require an intermediate solution HT of one hour at 1000-1010F to prevent eutectic melting of magnesium rich phases. Temper after natural aging is T4. Soak time 6-24 hours inclusive. Quench delay time begins when the furnace door starts to open and ends when the last corner of the load is in quenchant. Nominal thickness >.091" 15 seconds. Max quench delay times may be exceeded if all portions of the load will be above 775F when quenched.

    T6 300-320F for 1-6 hours. The time at temp will depend on time required for load to reach temperature. The times shown are based on rapid heating with soaking time measured from the time load reached minimum temp shown.
    With a 3/4" reach spark plug and the filled chambers the maximum section is about 1.25" thick, but that's not a very large section and the rest of the material is reasonably thin.

    There is a wide range between 12 hours and 6-24 hours for solution and 1-6 hours for againg and it would be nice to not have the oven running in the garage any longer than absolutely needed.

    I'd appreciate a recommendation on an appropriate time and temperature if someone has first-hand experience with this material.


  • #2
    I remember 175 degrees for 7 1/2 hrs then forced air quench, that's all I remember, the TTT graph is beyond me!, I've forgotten most of the crap in there, activation energy etc, here's a bit of light reading:
    Given the varied section thickness the thing will be different at the fin than the core anyway


    • #3
      Mark, I'll pass that document on to my pal who has the scientific background to grok it all. Thanks for sharing it.

      The paper seems mainly to be concerned with the artificial aging process, but that's the short term portion of the process. Solution time is the big question we have, what with the recommendations ranging from a flat 12 hours to some time within 6-24 hours.

      I can do 12 hours for our first try, but it would be nice to have a better idea whether that is good enough, or we'll need closer to 24 hours, or it is overkill and 6 hours is plenty. This paper mentions 6 hours

      I must admit that I'm surprised at the variation among the references. I'd thought that after all these decades and no doubt millions of tons of aluminum being processed that heat treatment would be a very cut and dried topic, at least for smaller castings.



      • #4
        It depends on analysis, the stuff bearing copper will reach temper on its own, I've age harden at room temp, forced ageing accelerates the process, refrigeration slows it, handy to know after annealing, throw it in the freezer it will stay soft, we used to do that with aircraft rivets, they were all colour coded too as a guide to what day they were annealed, I think there was a 4 day window for fabrication, old fashioned now as this was in the late 70s.
        I'm sorry I've forgotten most of the aluminium chemistry I knew, in the steel industry all we used Ali for was a deoxidant, the steel industry is still one of the Ali industry's best customers as all the steel is Aluminium killed, well nearly all, titanium and calcium are popular these days
        They reckon non ferrous heat treatment is an art not a science, getting temper right for bending was the worst, get it wrong and lovely orange peel would wreck it, or cracks but an engine block is going to be a bit more forgiving, allowing it the time it needs to age is as good as forced heat treat, about 10 days in a warm environment seems familiar, castings were stacked in the foundry behind the holding furnace
        See also homogenisation of Ali


        • #5
          " allowing it the time it needs to age is as good as forced heat treat, about 10 days in a warm environment seems familiar"
          I must be alum as 10 days in a warm environment sure sounds good. I took a hard fall sat on the wet ice & now it's just below zero, I hate winter