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Two near a titanium alloys, Ti-5.6Al-4.8Sn-.0Zr-1Mo-0.35Si (1#) and Ti-6.0Al-4.8Sn-2.0Zr-1Mo-0.35Si (2#), were solution-treated in the upper alpha+beta phase fields, and the duplex mixture microstructures consisting of the less volume fraction primary a phase (alpha(p)) and the transformed beta phase (beta(t)) were obtained. The aging treatments were carried out at 700 degrees C for 1# alloy and 760 degrees C for 2# alloy under varied terms, respectively. It guaranteed alpha(2) ordered phase to precipitated only in ap but not in beta(t) for the two alloys. The slower precipitation and growth of the a2 ordered phase and silicide was observed in 1# alloy in comparison with 2# alloy. The mechanical properties including tensile strength and ductility, the creep and lasting properties at 600 degrees C were investigated. Prolonging aging time did not predominantly change the tensile strength and ductility for the two alloys. The 600 degrees C/100 h thermal exposure caused a notable decrease of tensile ductility in 2# alloy though no distinct decrease could be observed in 1# alloy after. the thermal exposure. The lasting property of 1# alloy was increased with prolonging aging time and finally was equal to or even better than that of 2# alloy. Nevertheless, no evident increase emerged in 2# alloy with prolonging aging time. Similarly, the creep property of 1# alloy monotonously increased with increasing aging time and finally was equal to or even better than that of 2# alloy. No evident increase could be observed for 2# alloy. It can be deduced that the overgrowth of alpha(2) ordered phase and silicide is unable to enhance hot strength properties but cause an unacceptable damage to tensile ductility. The optimum equilibrium of the comprehensive properties depending on the proper control Of alpha(2) ordered phase and silicide can be achieved by properly selecting aging temperature and time.