Investigation on peripheral coarse grains and precipitation behavior of in-situ TiB2/Al-Cu-Mg composites with various Mg contents

As a primary alloying element, Mg strongly affects the microstructure and mechanical properties of Al matrix composites, while the corresponding mechanisms have not been clarified. In this study, the TiB2 reinforced Al-Cu-Mg composites with various Mg contents were fabricated following the procedures of salt-metal reaction, hot extrusion, solution, and peak aging. The results indicated that the surfaces of extruded composites were composed of fine dynamic recrystallized (DRXed) grains, while the subsurface mainly consisted of fibrous grains elongated along extrusion direction. Moreover, the depth of surface with fine DRXed grains increased with the increase of Mg content. The abnormal grain growth took place in the surface layer during the solution process, and the peripheral coarse grains (PCGs) appeared, since plenty of stored energy provided the driving force. The peak-aged composites had lots of T phases, and TiB2 particles were always well bonded with Al matrix. As the Mg content increased from 0.8 to 1.5 wt%, the quantity of evenly distributed S' phases increased, causing an increase of mechanical properties. However, when the Mg content was as high as 2.2 wt%, S' phases tended to concentrate on the T/Al interface or gathered together to form groups, resulting in the formation of precipitation free zones. Consequently, the hardness, ultimate tensile strength, and wear resistance were decreased.

Automated summary

The study found that Mg content strongly influences the microstructure and mechanical properties of TiB2 reinforced Al-Cu-Mg composites. Increasing Mg content results in deeper fine dynamic recrystallized grains on the surface and improved mechanical properties, but excessive Mg content can lead to the formation of precipitation free zones, ultimately reducing hardness and ultimate tensile strength.