Electric car underbody and preparation method thereof

The utility model relates to an electric car underbody and a preparation method thereof. The underbody comprises a panel and a framework. A middle cross beam and a rear cross beam are arranged in the middle and in the back of a car chassis respectively, a middle longitudinal beam is arranged between the middle cross beam and the rear cross beam, a left longitudinal beam and a right longitudinal beam are arranged on the left side and the right side of the car chassis respectively, and therefore a frame for installing a power battery cabin is formed. The panel and the framework are respectively made of a magnesium aluminum alloy composite material. The magnesium aluminum alloy composite material comprises 70-90% of magnesium aluminum alloy and 10-30% of inorganic filler. The magnesium aluminum alloy comprises 0.5-9% of Sn, 0.05-5% of Pb, Sr, Sb, Te, 40-60% of Mg and 40-60% of Al, wherein the percentage of Sr is smaller than or equal to 2%, the percentage of Sb is smaller than or equal to 0.2%, and the percentag