An　Al0.5CoCrFeNiSi0.2　high-entropy　alloy　was　prepared　by　vacuum　arc　melting.　The　alloy　was　aged　from　700　to　1100 °C.　The　effects　of　aging　on　the　phase　transformation　and　mechanical　performances　were　explored.　The　as-cast　alloy　showed　a　dendritic　(DR)　microstructure.　The　DR　region　was　an　Fe,Cr-rich　FCC　phase,　while　the　interdendritic　(ID)　region　was　a　spinodal　structure　composed　of　Fe,Cr-rich　BCC　(A2)　and　Ni,Al-rich　BCC　(B2)　phases.　At　aging　temperatures　between　700　and　900 °C,　the　Fe,Cr-rich　BCC　(A2)　phase　in　the　ID　region　transformed　into　σ　and　Fe,Cr-rich　FCC　phases.　Meanwhile,　some　Ni,Al-rich　FCC　phase　particles　precipitated　from　the　DR　region.　During　aging　at　1100 °C,　the　DR　microstructure　disappeared,　and　a　microstructure　composed　of　Fe,Cr-rich　FCC　and　Ni,Al-rich　BCC　(B2)　phases　both　possessing　a　lamellar　shape　was　developed.　The　alloy　exhibited　evident　hardening　and　lower　tensile　strain　when　the　aging　temperature　was　lower　than　1000 °C,　which　was　mainly　attributed　to　the　generation　of　the　σ　phase　in　the　ID　region.　However,　a　contrasting　behavior　was　observed　when　the　aging　temperature　was　higher　than　1000 °C,　which　was　attributed　to　the　redissolution　of　the　σ　phase　and　the　microstructure　coarsening.　©　2015,　ASM　International.