The　influence　of　age　hardening　treatment　on　the　hardness　and　microstructure　of　semi-solid　squeeze　cast　A319　alloy　is　investigated.　At　175 °C,　the　age-hardening　curve　of　the　alloy　shows　two　peaks　between　which　there　was　an　apparent　valley.　Analyses　by　transmission　electron　microscopy,　selected　area　electron　diffraction　and　energy-dispersive　X-ray　detection　suggest　that　the　first　peak　is　caused　by　formation　of　G.P.2　zones　while　the　second　peak　can　be　related　to　formation　of　the　metastable　θ′-　and　Q′-phases.　Compared　with　gravity　die　cast　A319　the　semi-solid　squeeze　cast　A319　shows　a　larger　increase　and　a　higher　peak　in　hardness　during　the　age　hardening　process.　Additionally,　the　latter　requires　another　32　h　to　reach　the　first　hardness　peak　while　it　reaches　the　second　hardness　peak　about　24　h　earlier　than　the　former.　©　2018　Wiley-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim