A lightweight automobile brake disc (10) and a preparation method therefor. A disc cap (110) of the lightweight automobile brake disc (10) is prepared from a first aluminum-based material with good processibility, and a disc body (120) is prepared from a second aluminum-based material with good wear resistance and heat resistance. By controlling the alloy element content of an aluminum alloy matrix in the first aluminum-based material to be smaller than or equal to the alloy element content of an aluminum alloy matrix in the second aluminum-based material, the sintering shrinking percentages of the two materials during a preparation process, in which a powder metallurgy method is used, are matched.

A method for friction stir forming a metal matrix composite (MMC) structure (76). The method includes the step of providing a substrate (12) comprising a metallic material and securing a preformed MMC layer (14, 16) comprising an MMC material in a position overlying at least a portion of the substrate (12). The method further includes the step of friction stirring the preformed MMC layer (14, 16) with a friction stirring tool (50) which includes a rotating probe (56), including locating the probe (56) at a stirring depth at which the probe (56) extends through the preformed MMC layer (14, 16) into a portion of the substrate (12) and passing the tool (50) through the preformed MMC layer (14) at the stirring depth to friction stir the preformed MMC layer (14, 16) and integrate the preformed MMC layer (14, 16) with the substrate (12).

A thixomolding material includes: a metal body that contains Mg as a main component; and a coating portion that is adhered to a surface of the metal body via a binder and contains SiC particles containing SiC as a main component. A mass fraction of the SiC particles in a total mass of the metal body and the SiC particles is 2.0 mass % or more and 40.0 mass % or less. The binder may contain waxes. A content of the binder may be 0.001 mass % or more and 0.200 mass % or less.