In our foundry we cast aluminum at about 730 Celsius. At this temperature some of the magnesium burns off. We use A356 with an optimum Mg content of .33% When it is necessary to add Mg to compensate for burn-off, we add alloy sheets of 75% Al and 25% Mg. the low Mg concentration is for safety and stability, but even these will burn in a hotter furnace.
A356 is 92% Al, 7% Silicon, .33% Mg, not less than .10% Ti and not more than .25% Fe. The balance is trace amounts of Chromium, Nickel, Manganese, Copper and Tungsten. By contrast with the Mg, Titanium tends to settle out of the molten bath at about the same rate the Magnesium burns off. The metal must be "stirred" to re-suspend the Ti in the alloy.
If you have a compound bow with a cast riser, odds are it is made of an aluminum-magnesium alloy with the mag being around 10% (IIRC). I'm sure there are different alloys used in machined-riser bows.