This　paper　investigated　the　microstructure　and　hardness　of　the　cold　rolled　AlSi9Mg　aluminum　alloy　after　the　heating　at　different　maintained　(semi-solid)　temperatures　with　different　duration　times.　The　effects　of　process　parameters　on　the　microstructural　evolution　and　hardness　of　semi-solid　alloy　were　investigated.　Results　showed　that　the　increase　in　the　maintained　temperature　enlarged　both　the　average　grain　size　and　the　shape　factor.　The　average　grain　size　also　increased　when　the　duration　time　increased.　The　shape　factor　increased　first　and　then　decreased　with　the　increase　in　the　duration　time　at　the　maintained　temperature　of　560　and　565°C.　However,　the　shape　factor　kept　improved　with　increasing　the　duration　time　at　the　maintained　temperature　of　570°C.　The　coarsening　of　solid　grains　in　the　microstructure　resulted　from　the　coalescence　and　Ostwald　ripening　mechanisms.　The　latter　one　played　a　more　significant　role　when　the　maintained　temperature　or　the　duration　time　increased.　The　hardness　of　semi-solid　AlSi9Mg　alloy　decreased　with　the　increase　in　the　duration　time　or　the　temperature.　The　parameters　in　the　Hall-Petch　and　the　Lifshitz-Slyozov-Wagner　relationships　for　the　semi-solid　alloy　were　identified.　The　coarsening　rate　of　solid　grain　at　560,　565　and　570°C　were　85.47,　1177.93　and　1357.2μm3/s,　respectively.　©　2020　Japan　Institute　of　Metals　(JIM).　All　rights　reserved.