Study on the microstructure and mechanical properties of hot rolled nano-ZrB2/AA6016 aluminum matrix composites by friction stir processing

Abstract

In this paper, in-situ ZrB2/AA6016 particle-reinforced aluminum matrix composites were prepared in molten A6016 aluminum alloy melt by KBF4-Al- K2ZrF6 reaction system. For the first time, this paper presents that after casting, the composites would be subjected to large strain hot rolling (LSHR) with 60 % undercutting and then friction stir processing (FSP) with a stirred probe speed of 1200 r/min and a traveling speed of 60 mm/min. To study the microstructure and mechanical properties of composites strengthened by large strain hot rolling combined with friction stir processing. The results show that the tensile strength of the base material is 140.1 MPa, the elongation is 46.3 %, the product of strength and elongation reaches 6.5 GPa%, and the average hardness is 43.4 HV; The tensile strength of LSHR+FSP nugget zone is 163.4 MPa, the elongation is 78.9 %, the product of strength and elongation reaches 12.9 GPa %, which is about 98.6 % higher than the base material, and the average hardness is 59.8 HV, which is about 37 % higher than the base material. SEM, EBSD, and TEM analyses showed that the average grain size is refined from 189.7 μm to 3.8 μm after LSHR+FSP. The ZrB2 particles are sufficiently fragmented, with a particle size of about 20 nm, and uniformly dispersed in the matrix. This study provides the theoretical and experimental basis for applying nanoscale ZrB2 particles reinforcing ultrafine crystalline aluminum matrix composites prepared by LSHR + FSP.