Significant improvement of the room and cryogenic mechanical properties of an AlN particle reinforced Al matrix composite by alloying element magnesium

Nowadays, the mechanical properties of aluminum alloys have been studied extensively, but the study of aluminum matrix composites (AMCs) at extreme temperatures, particularly at cryogenic temperatures, is rare. In this work, an AlNp reinforced AMCs with excellent room and cryogenic temperature mechanical properties was manufactured by adding magnesium, and the corresponding microstructure evolution and strengthening mechanisms were systematically investigated. There are two kinds of particles in AlNp/Al, the small AlNp and the large AlB2p. With the Mg content increased, the AlNp became more dispersed and the AlB2p transformed into AlMgB4p. In addition, Mg atoms also dissolved in the matrix, which played a positive role in improving the mechanical properties. The ultimate tensile strength of the composites at RT was increased to 317 MPa, 419 MPa, and 485 MPa from 251 MPa after adding 1, 3, and 5 wt% Mg respectively. The cryogenic strength was further increased to 519 MPa, 592 MPa, and 611 MPa from 469 MPa, while keeping a decent ductility of about 5.6%, which was due to the more uniform microstructure avoiding crack generation.