Research on high strength and creep behavior of in-situ (Al2O3 + ZrB2)/7055 Al nanocomposites

Abstract

In this study, to achieve high strength, high ductility and good creep resistance, in-situ Al2O3 and ZrB2 nanoparticles were introduced into 7055 aluminum alloy subjected to the deformation of hot rolling. The interface between nanoparticles and Al matrix displayed tightly-bonded and there were orientation relationships (ORs) between them: 1¯2¯4¯Al2O3//2¯1¯1¯Al,(021)Al2O3//(111)Al, 020ZrB2//022¯Al. The precipitates were easy to nucleate at the interface than in the matrix due to the low energy barrier to overcome. Precipitates like η and Al2Cu had the ORs with the matrix: 112¯3η//11¯0Al, [111]Al2Cu//[110]Al. The nanoparticles along with the precipitates had the effect of both promotion and inhibition to the recrystallization process. The particle-induced improvement for the strength was due to the excellent work-hardening ability. Moreover, mechanical performance of the (Al2O3 + ZrB2)/7055 Al nanocomposites exhibited the tensile strength of 749 MPa and the elongation of 21.81%, which indicated 14.3% and 11.8% higher than the matrix. The plastic zone and dislocation punched zone of the nanoparticles had been calculated during the crack process. The Al2O3 and ZrB2 nanoparticles indicated the high-temperature creep resistance ability with the steady creep rate of the (Al2O3 + ZrB2)/7055 Al composites 6– 17 times higher than the matrix, in which the values of apparent stress exponent (n), apparent activation energy (Q) and threshold stress were 9.48, 374.13 kJ/mol and 50.13 MPa, respectively. The stress exponent of 5 suggested that the dislocation climb was dominative in creep process. In addition, the strengthening contributions, toughness mechanism and creep behavior were discussed.