Effects of Sn Microalloying on the Microstructure and Properties of Al-Mg-Mn-Si Alloy

Microalloying with Sn is a pivotal strategy for enhancing the strength and thermal stability of Al-Mg-Mn-Si alloys by enabling microstructural optimization. This study systematically investigates the influence of 0.1 wt.% Sn on an Al-4.0Mg-1.0Mn-0.2Si alloy through a comparative analysis with a Sn-free counterpart. The experimental methodology included isochronal aging and isothermal aging, room-temperature tensile testing, electrical conductivity measurements, and detailed microstructural characterization via transmission electron microscopy (TEM) and optical microscopy (OM). The results unequivocally demonstrate that Sn addition significantly enhances the alloy’s microhardness, tensile properties, and heat resistance. Specifically, the Sn-containing alloy (1#) achieved a peak hardness of 98.4 HV during a three-stage aging process, which is 14.1% higher than the 84.5 HV of the Sn-free alloy (2#). In the as-rolled state, alloy 1# exhibited ultimate tensile strength (UTS) and yield strength (YS) of 397 MPa and 344 MPa, representing increases of 20.2% and 15.7%, respectively, without compromising ductility. Microstructural analysis revealed that the enhancement is attributed to the Sn-promoted formation of finely dispersed α-AlMnSi precipitates. These precipitates effectively pin dislocations, strengthening the alloy, and simultaneously suppress recrystallization nucleation and growth, thereby elevating the recrystallization temperature and improving overall heat resistance. This work confirms that microalloying with Sn is an effective strategy for developing high-performance Al-Mg-Mn-Si alloys with superior mechanical properties and thermal stability.