Achieving ultra-high strength in Be/Al composites by self-exhaust pressure infiltration and hot extrusion process

Beryllium particle reinforced aluminum matrix (Be/Al) composite with exceptionally high strength was fabri-cated from Be debris by self-exhaust pressure infiltration and hot extrusion process. The microstructures char-acteristics and mechanical properties of the Be/Al composite at as-cast and as-extruded state were systematically investigated in the current study. It was found for the as-cast composite that uniform distribution of beryllium particles with average size of 2.2 mu m were achieved, the microcracks in beryllium particles were repaired in situ by infiltrating liquid aluminum into these microcracks under external pressure. The Be phase and Al phase were well bonded despite the presence of nano BeO at the interface. After hot extrusion, the beryllium particle deformed and elongated along the extrusion direction. The average grain size of Al was refined from hundreds of microns to 450 nm, and the dislocation density increased significantly. The tensile strength and yield strength of Be/Al composite reached 595 MPa and 494 MPa by hot extrusion, respectively. The ultra-high strength was mainly related to grain boundaries strengthening, dislocation strengthening, precipitation strengthening and load transfer strengthening. Compared with the composites prepared by the investment casting and powder metallurgy methods, the Be/Al composite showed more than 100% increment in strengthening efficiency and 80% increment in yield strength. It indicated that the self-exhaust pressure infiltration technology combined with hot extrusion process was a feasible and successful method to prepare high performance Be/Al composites.