Melting aluminum for casting requires heating the metal to at least 1,220°F (660°C) in a crucible placed inside a furnace, then pouring the molten metal into a mold at 1,300 to 1,400°F. The process is straightforward once you understand the equipment, the right scrap to use, and the safety precautions that keep a fun hobby from turning dangerous.
Choose the Right Scrap Aluminum
Not all aluminum melts and casts equally. The single best source for hobby casting is scrap automotive castings: old alloy wheels, transmission housings, engine blocks, and cylinder heads. These are typically made from A356 or similar casting alloys that contain silicon, which makes molten aluminum flow more easily into mold details and machines cleanly afterward. Car manufacturers already optimized these alloys for casting, so you’re essentially recycling a proven formula.
Soda cans and extruded aluminum (window frames, bar stock, tubing) will melt, but they create problems downstream. Extruded alloys are “sticky” when you try to file, drill, or sand the finished casting. They also produce more dross (the crusty oxide layer that forms on the melt surface) because cans are thin, coated in paint and plastic liners, and have a high surface-area-to-volume ratio. If cans are all you have, they’ll work for rough parts that don’t need finishing. For anything you plan to machine or polish, stick with cast aluminum scrap.
Furnace Options for Home Melting
Three furnace types dominate small-scale aluminum casting: propane, charcoal, and electric resistance. Each has real tradeoffs beyond just price.
Propane furnaces are the most popular choice for backyard casters. A steel body lined with refractory cement, fed by a standard propane burner, can reach aluminum pouring temperatures in 15 to 30 minutes depending on the charge size. They’re relatively cheap to build or buy, and propane is available everywhere. The downside is metal quality. Combustion gases pass over the crucible and react with molten aluminum, forming aluminum oxide dross and introducing hydrogen gas into the melt. Gas-fired crucible furnaces typically lose 3% to 5% of your metal to dross, compared to just 1% to 1.5% in electric furnaces. The castings also tend to have more internal porosity from trapped hydrogen bubbles.
Charcoal furnaces are the cheapest entry point. A steel bucket, some refractory lining, a hair dryer for forced air, and a bag of lump charcoal will get aluminum molten. They’re slow, dirty, and hard to control temperature-wise, but they work and cost almost nothing to set up. Expect the same dross and gas issues as propane, plus more ash contamination.
Electric resistance furnaces produce noticeably better castings. Without combustion gases hitting the melt, the metal stays cleaner for longer. In comparative testing, electrically melted aluminum reached tensile and yield strengths about 20% higher than gas-melted samples, with far more consistent mechanical properties. The gas-melted test bars almost always broke at a dross inclusion or hydrogen bubble, while electric-melted bars rarely showed those defects. Electric furnaces run at 75% to 80% energy efficiency versus a fraction of that for gas-fired units, which lose enormous heat through their flues. The catch is upfront cost, which is significantly higher for a quality electric furnace.
For most beginners, a propane furnace hits the sweet spot of cost, speed, and results. Upgrade to electric if you start caring about casting quality and consistency.
Picking a Crucible
The crucible sits inside your furnace and holds the molten aluminum. Two materials dominate: silicon carbide graphite and clay graphite.
Silicon carbide graphite crucibles handle the job better for aluminum. They conduct heat efficiently, resist thermal shock (the stress of rapid heating and cooling), and stand up to the chemical erosion that molten aluminum causes over time. They cost more but last significantly longer. Clay graphite crucibles are cheaper and work fine for lower-temperature metals like gold and silver, but they’re less durable at the sustained high temperatures aluminum requires. For aluminum casting, a silicon carbide graphite crucible in the #4 to #10 size range (holding roughly 4 to 10 pounds of aluminum) is the standard recommendation for hobby work.
Melting Temperatures and Alloy Differences
Pure aluminum melts at exactly 1,220.58°F (660.32°C), but you’ll rarely work with pure aluminum. Alloys have a melting range rather than a single melting point, meaning the metal transitions through a partially solid, partially liquid state. This effect is called melting point depression, and the alloying elements can lower the starting temperature significantly.
Common casting alloys melt at lower temperatures than pure aluminum. A380, one of the most widely used casting alloys, begins melting at just 1,000°F (538°C) and is fully liquid by 1,100°F (593°C). A360 melts between 1,030 and 1,100°F (557 to 596°C). If you’re melting scrap automotive parts made from these alloys, you won’t need as much heat as you might expect.
Wrought alloys from extruded stock have wider melting ranges. 6061 melts between 1,080 and 1,205°F (580 to 650°C), while 7075 starts softening as low as 890°F (475°C). This variation is why experienced casters prefer to melt known alloys rather than mystery scrap. When you mix alloys randomly, you get unpredictable flow behavior and casting quality.
Target Pouring Temperature
Getting aluminum molten isn’t enough. You need it hot enough above its melting point to flow into all the details of your mold before it starts solidifying. The ideal pouring temperature for most aluminum castings is between 1,300 and 1,400°F (700 to 760°C), depending on the size and complexity of the part. Smaller, thinner-walled parts need the higher end of that range because the metal cools faster in a thin section. Larger, simpler shapes can be poured closer to 1,300°F.
Pouring too hot causes its own problems: more shrinkage as the metal cools, more hydrogen absorption from atmospheric moisture, and more dross formation. Pouring too cool gives you incomplete fills and cold shuts (visible seams where two streams of metal met but didn’t fuse). A simple infrared thermometer or thermocouple probe designed for molten metal takes the guesswork out of it.
Dealing With Dross and Gas
Every time you melt aluminum, a layer of aluminum oxide dross forms on the surface. This grayish, crusty skin traps good metal underneath it. In industrial settings, salt-based fluxes (mixtures of sodium chloride and potassium chloride) are added to break up the oxide films and let trapped aluminum droplets coalesce back into the melt. Small amounts of fluoride compounds improve the flux’s ability to wet the oxide and separate it from clean metal. For hobby casting, commercial aluminum flux is sold in small containers. You sprinkle it on the surface, stir gently, let it work for a minute or two, then skim the dross off with a slotted steel spoon before pouring.
Hydrogen porosity is the other enemy of clean castings. Molten aluminum absorbs hydrogen from moisture in the air, combustion gases, and even damp tools. When the metal solidifies, that dissolved hydrogen forms tiny bubbles trapped inside the casting. Industrial foundries remove hydrogen by bubbling inert gas (nitrogen or argon) through the melt. The dissolved hydrogen migrates into the inert gas bubbles and gets carried to the surface. For small-scale work, the simplest prevention is keeping everything dry: preheat your tools, your mold, and your scrap before they contact the melt. Wet or damp anything near molten aluminum is both a quality problem and a safety hazard.
The Water and Moisture Danger
This is the single most important safety point in aluminum casting. When molten aluminum contacts water, the water flashes to steam instantly, expanding to roughly 1,600 times its liquid volume. This can launch molten metal in every direction. These steam explosions are violent and unpredictable. Research at Oak Ridge National Laboratory has studied these melt-water interactions extensively, examining how surface conditions, melt temperature, water temperature, and external shocks all contribute to triggering explosive events.
Prevention is straightforward but non-negotiable. Never place any damp or wet material into molten aluminum, period. This includes scrap that’s been sitting in rain, tools that haven’t been preheated, molds with residual moisture, and concrete floors (which contain trapped water and can spall explosively if metal spills on them). Work on dry sand or bare dirt. Preheat all tools and scrap by placing them near the furnace before they go into the melt. Keep a dry sand bucket nearby for spills rather than a fire extinguisher, since some extinguisher types contain water.
The Basic Melting Process
Once your equipment is assembled, the actual process follows a consistent sequence. Start your furnace and let the crucible preheat empty for a few minutes. This reduces thermal shock on the crucible and burns off any residual moisture. Add your aluminum scrap in small batches rather than loading the crucible full at once. Smaller pieces melt faster and pack more efficiently. As each batch melts down, add more until you have enough molten metal for your pour.
When the aluminum is fully liquid and up to temperature (check with a thermocouple or infrared thermometer), add flux if you’re using it, stir gently, and skim dross from the surface. Preheat your pouring ladle or lifting tongs by holding them near the furnace opening. Lift the crucible smoothly and pour in a steady stream into the sprue (the funnel-shaped opening) of your mold. Pour continuously without stopping and starting, which introduces turbulence and trapped air.
Let the casting cool naturally in the mold. Quenching a fresh casting in water can cause cracking from thermal shock, and depending on the alloy, it can alter the metal’s hardness in ways you didn’t intend. Once cool, break away the mold material, cut off the sprue and any risers, and you have a raw casting ready for finishing.