Synergistic effect of joint addition of Sb plus Mn on high temperature strengthening in Al-4Cu heat-resistant alloy

The synergistic effect of joint addition of Sb + Mn on high temperature strengthening in Al-4Cu heat-resistant alloy was studied by sole and joint addition of Sb and Mn and tensile test at 300 C. The microstructure evolution of the precipitation particles during the LTHE treatment (a long-time heat exposure at 300 ? for 100 h) was characterized by TEM-SAED and Elements-Mapping to reveal the high temperature strengthening mecha-nisms. It is found that the joint addition of trace Sb + Mn leads to an overflowing superimposition effect that significantly increase the values of sigma 0.2 at 300 ? in T5 and LTHE states. In Al-4Cu alloy, Sb micro-alloying can promote the precipitation of theta' phases, however, during the LTHE treatment the phase transformation from theta' to theta cannot be suppressed by it. Elements-Mapping images of Mn element strongly demonstrate that, during the LTHE treatment, Mn atoms are increasingly enriching in front of the growth interface of theta' particles. This enrichment hinders the coarsening of theta' particles and hence suppress the phase transformation from theta' to theta during the LTHE treatment. It is the synergistic effect of Sb-induced promotion on the precipitation of theta' particles and Mn-induced suppression on the coarsening of theta' particles and phase transformation from theta' to theta that leads to high density of fine theta' particles still existing in the Al matrix after the LTHE treatment which still significantly strengthen the matrix. Therefore, the alloy with the joint addition of Sb + Mn has the highest value of sigma 0.2 at 300 ? in LTHE state among the studied alloys.

Automated summary

The synergistic effect of joint addition of Sb and Mn on high temperature strengthening in Al-4Cu heat-resistant alloy was investigated. The addition of trace amounts of Sb and Mn significantly increased the values of sigma 0.2 at 300°C in T5 and LTHE states. The microstructure evolution of the precipitation particles was characterized and it was found that Sb promoted the precipitation of theta' phases while Mn suppressed the coarsening and phase transformation from theta' to theta. The joint addition of Sb and Mn resulted in a high density of fine theta' particles after the LTHE treatment, which effectively strengthened the matrix.