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A new joining process for magnesium alloys, rotation friction drilling riveting (RFDR), is proposed in this paper. In RFDR operation, a semitubular rivet with a grip rod and a rivet cap rotating at high speed is brought to contact with the riveted sheets, generating frictional heat between the rivet and riveted sheets, which softens the sheet materials and enables the rivet to be drilled into the sheets under reduced force. While being inserted, the rivet pierces through the top sheet and flares into the bottom sheets due to the action of the cavity die, thereby forming a mechanical interlock between the rivet and riveted sheets. Our studies showed that RFDR of the magnesium alloy sheets could be carried out at room temperature and provided the joints with superior shear strength and fatigue property when compared with self-piercing Hveting (SPR). The effects of the operating parameters of the RFDR process on the quality of the joints were also investigated in the study. The results showed that while the rivet rotating speed little affected the shear strength of RFDR joints, the rivet shank length and the downward pressure had a significant influence on the mechanical properties of the RFDR joints. Therefore, it is very important to choose the right rivet shank length and downward pressure for producing RFDR joints with high quality. [ABSTRACT FROM AUTHOR]

A surface functionalization combined powder metallurgy strategy was used to fabricate the uniformly distributed nanodiamond (ND) reinforced ND/2024Al composites. A variety of tests confirmed that surface functionalization could reduce the amorphous carbon and assemble more functional groups on NDs, which can help NDs de-agglomerate and disperse uniformly on the surface of aluminum powders. SEM and TEM observations showed that SF is beneficial for uniformly dispersing NDs in the aluminum matrix, encapsulating more NDs in the grains, and forming a better interfacial bond with aluminum. Mechanical tests showed the strength and elongation of the functionalized ND/2024Al composite were simultaneously enhanced. Theoretical estimation and experimental measurement show that the strength improvement from surface functionalization is mainly due to the enhancement of Orowan strengthening and thermal mismatch strengthening. This work offers new insight into the design and fabrication of ND-metal matrix composites (MMCs) with high strength and ductility. • Surface functionalization (SF) purifies NDs and introduce functional groups on their surface. • SF disperses NDs in α-Al matrix and increases its interfacial bonding with matrix. • SF disperses more NDs within the grains rather than grain boundaries of α-Al matrix. • SF simultaneously enhances strength and ductility of ND/2024Al composites. [ABSTRACT FROM AUTHOR]