The micro-texture, grain size, morphology, size and distribution of the second phase in 6063 Al alloys significantly influence the comprehensive mechanical properties of alloys. By adding Sr to the 6063 Al alloys, this study performed a comparison of the effect exerted by micro-texture and grain refinement and explored the existence of Sr and its influence on the second phase. Inaddition, the influence mechanism for mechanical properties of the Sr-added alloys was also investigated. The results show that the phase structure of 6063 Al alloys is changed after adding Sr The Al₂Si₂Sr intermetallic compound is formed, and numerous substructures are developed during dynamic recovery and recrystallization. Moreover, after adding Sr element, the grain size of 6063 Al alloys is reduced from 33.45 μm to 24.04 μm. Small-angle grain boundaries increase, while large-angle grain boundaries decrease. Sr element changes the micro-texture of 6063 Al alloys significantly when Cube{100}〈001〉, Goss{110}〈001〉 and S {123}〈634〉 become Cube{100}〈001〉. The tensile strength, yield strength and Brinell hardness of 6063 Al alloys increase by 59.67%, 69.36% and 36.63%, respectively. Taken together, the Sr element strengthens the mechanical properties of 6063 Al alloys through fine-grained strengthening.

The as-cast Al-4.6Mg alloy was subjected to deformation and sensitization–desensitization heat treatment, and then the microstructure and the enhancement mechanism of Sr were investigated by optical microscopy, scanning electron microscopy–energy-dispersive spectroscopy, electron backscatter diffraction, and transmission electron microscopy. The precipitation phases of Al-4.6Mg alloy were mainly β-Al₃Mg₂, Al₆Mn, and Al₆(Mn Cr), and the nanoscale precipitation phases were Al₃Mn and Al₁₁Mn₄. The formation of β-Al₃Mg₂ was hindered by the addition of 0.1 wt.% Sr. In addition, the precipitate phase Al₄Sr and the nano-sized precipitate phase τ-Al₃₈Mg₅₈Sr₄ were uniformly distributed in the spherical matrix. The addition of Sr promoted the redissolution of Mg atoms in Al-4.6Mg alloy, increasing the solubility of Mg in the α-Al matrix from 4.7 wt.% to 5.1 wt.%. The microstructure analysis showed that Sr addition inhibited the recovery and recrystallization of the alloy because the Sr element elevated the recrystallization temperature. As a result, the grain deformation was intensified, the grain size was decreased from 6.96 μm to 5.39 μm, the low-angle grain boundaries were increased from 78.7 at % to 84.6 at %, and the high-angle grain boundaries were increased from 21.3 at % to 15.4 at %. Furthermore, the mechanical properties of the alloy were significantly improved, and the plasticity degraded after the addition of the Sr element. The yield strength of the alloy was enhanced mainly through fine grain strengthening, dispersion strengthening, solid solution strengthening, and working hardening. The strengthening mechanisms were analyzed in detail.