Edge-to-edge matching (E2EM) model was used to predict the potency of LaB₆ as the heterogeneous nucleation substrate for primary Al₁₃Mn₄Si₈ phase formed during the solidification of Al-Si-Cu-Mn heat-resistant alloy. There are five pairs of orientation relationships (ORs) between LaB₆ and Al₁₃Mn₄Si₈ phases which meet the criteria of E2EM model. One pair of plane ORs ((110)_LaB6//(110)_Al13Mn4Si8) are demonstrated by TEM observation. This strongly indicates that the LaB₆ phase can act as the heterogeneous nucleation substrate for the primary Al₁₃Mn₄Si₈ phase. 1.0 wt.% of Al-2La-1B master alloy was also added into Al-12Si-4Cu-2Mn alloy to evaluate the refining effect by microstructure observation and tensile test. Experimental results show that addition of Al-2La-1B master alloy can significantly refine the primary Al₁₃Mn₄Si₈ phase, supporting the prediction accuracy of E2EM model. However, such refinement of primary Al₁₃Mn₄Si₈ phase does not lead to an improvement in strength. This is due to the larger difference in elastic modulus between the finally formed Al₁₃Mn₄Si₈ phase and aluminum matrix than that of Al₁₅Mn₃Si₂ phase.