<p>The 6061 aluminum alloy (AA6061) is widely used in aerospace, automotive manufacturing, and electronic devices due to its excellent properties. As an advanced process integrating the advantages of casting and forging, semi-solid processing (SSP) technology can significantly improve the comprehensive properties of aluminum alloys. To address the difficulty in accurately predicting the deformation behavior of AA6061 in the two-phase region, isothermal compression tests were performed using a thermal simulator (THERCMESTOR-Z/100). Tests were conducted at strain rates of 0.01 to 10&#xa0;s⁻¹ and temperatures of 580&#xa0;°C to 610&#xa0;°C, and the corresponding stress-strain data were obtained. Meanwhile, combined with the analysis of the microstructure evolution law of AA6061, it was found that the presence of liquid phase plays a crucial role in the rheological behavior of the alloy in the two-phase region. Based on this, this paper constructed a modified Arrhenius model and a Fields–Backofen (FB) model by introducing a liquid volume fraction adjustment factor. The model accuracy was evaluated by the Average Absolute Relative Error (AARE) and coefficient of determination (<i>R</i>²). The results show that the AARE of the strain-compensated Arrhenius model was 16.1 pct, and the AARE of the Arrhenius model considering liquid volume fraction modification was 7.0 pct, with the prediction accuracy improved by 56.5 pct. The AARE of the FB model considering liquid-phase modification was 5.7 pct, which was the model with the highest prediction accuracy in this study, because the FB model further considered the piecewise characteristics of the stress-strain curve. The modified constitutive models significantly enhance the ability to describe the complex rheological behavior under non-equilibrium solidification conditions, providing theoretical support for the optimization of semi-solid processing windows and numerical simulation.</p>