Die Casting

Integrated die casting has been called a revolution in body-in-white manufacturing. A traditional car body is welded together from dozens or even hundreds of parts; integrated die casting forms them in a single shot. There are fewer weld points, less weight, and torsional stiffness improves by 20% to 30%.

But this technology has a fatal bottleneck.

Conventional die-cast aluminum alloys, such as the commonly used AlSi10MnMg, don't deliver sufficient mechanical properties as-cast. They must undergo T6 or T7 heat treatment—high-temperature solution treatment, quenching, and artificial aging—before strength and toughness meet requirements. That's exactly where the problem lies: integrated die-cast parts are large and thin, with walls perhaps only a few millimeters thick but dimensions covering an entire rear body structure. Put such a part into a heat treatment furnace, and it distorts easily at high temperature; during quenching, it outright cracks or warps. It then has to be straightened and corrected, driving the scrap rate extremely high.

So if the material cannot be "heat-treatment-free," integrated die casting simply doesn't work in physical terms. You cannot throw a one-to-two-meter-long thin-walled aluminum part into a furnace, heat it, quench it, and still expect it not to deform.

Heat-treatment-free aluminum alloys solve exactly this problem. In the as-cast state—meaning the part cools directly after die casting, with no heat treatment whatsoever—they already meet the mechanical property requirements for structural body parts. Zeekr's "Fiber Crystal" series of heat-treatment-free aluminum alloys achieves, in the as-cast state, a tensile strength of 260 MPa, yield strength of 125 MPa, and elongation above 12%. They have been used in the integrated die-cast bodies of models such as the Zeekr 9X, 009, and 7X. Patent data show that such materials can reach a yield strength above 285 MPa with elongation exceeding 2.5%.

The essence of heat-treatment-free technology lies in designing the alloy composition so that strengthening phases precipitate directly during the rapid solidification of die casting, rather than being slowly "cultivated" through subsequent heat treatment. Conventional heat treatment relies on solution treatment to dissolve alloying elements into the aluminum matrix, then aging to precipitate nanoparticles for strengthening. Heat-treatment-free materials build this step into the die-casting cooling process itself, using specific ratios of Si, Mg, Mn, Zn, and other elements, combined with the rapid solidification conditions of high-vacuum die casting, so that strengthening phases form in the as-cast state.

Without heat-treatment-free materials, integrated die casting could only remain a concept. With them, it becomes possible to eliminate the heat treatment furnace, skip the straightening process, and raise the good-part rate from "virtually zero" to over 90%. Precisely for this reason, the formulations of heat-treatment-free aluminum alloys were long monopolized by overseas companies, making them one of the hardest "chokepoint" links in the entire supply chain. Only after domestic companies made successive breakthroughs did integrated die casting truly move from "affordable equipment" to "buildable parts."

In one sentence: Integrated die casting determines what a car body can become; heat-treatment-free materials determine whether it can be made at all.