Aluminum and Injection Molding: What Buyers Actually Source Instead

Injection molding pushes molten polymer into a steel cavity at 200-400°C and a few thousand psi. Aluminum alloys like 6061-T6 and 7075-T73 are wrought materials whose strength comes from cold work and heat treatment, not from being poured. There is no thermoplastic analog: you cannot soften 6061 to a viscous paste and inject it without fully liquefying it, at which point you have a casting operation, not molding. The -T6 and -T73 tempers are also the entire point of choosing those alloys. 6061-T6 reaches roughly 310 MPa yield because it was solution treated and artificially aged. Melt it and you have thrown that microstructure away. So when a buyer says "injection mold this 6061 bracket," the honest answer is that the part is either machined from billet, die cast from a casting alloy, or, for small high-volume parts, made by metal injection molding using aluminum powder feedstock.

Metal injection molding is the one process that genuinely combines injection molding mechanics with metal. Fine aluminum powder is blended with a polymer binder, injected into a mold exactly like plastic, then debound and sintered. The result is a near-net-shape metal part with 95-98% density. Aluminum MIM is far less common than steel or stainless MIM because aluminum's tenacious oxide skin resists sintering, so most aluminum MIM uses specialized alloys and controlled atmospheres. MIM makes sense for small, complex parts in runs above roughly 10,000 pieces, where the per-part price drops to a few dollars and tooling amortizes. Typical part size stays under 100 grams. If your aluminum part is a tiny intricate component, MIM is worth quoting. If it is a structural bracket, MIM is the wrong tool and you want machining or die casting instead.

When volumes are high and geometry is complex, aluminum die casting is what buyers usually want. Casting alloys like A380, ADC12, or A356 are injected into hardened H13 steel dies at pressures of 10,000-15,000 psi. These are not the wrought 6061/7075/2024/5052 grades from the request, and that substitution matters: A380 has excellent castability but lower ductility than 5052 sheet, so the design has to suit casting. Die casting holds tolerances around ±0.1 mm on small features and produces as-cast surface finishes of 32-63 µin Ra. It is the right call for housings, brackets, and enclosures at 5,000+ parts a year. Tooling runs $15,000-$80,000 depending on size and complexity, which is why it only pencils out at volume.