3004　Aluminum　alloy　has　been　subjected　to　tension　test　at　a　range　of　strain　rates　(5.56　x　10(-5)　to　5.56　x　10(-3)　s(-1))　and　temperatures　(233-573　K)　to　investigate　the　effect　of　temperature　and　strain　rate　on　its　mechanical　properties.　The　serrated　flow　phenomenon　is　associated　with　dynamic　strain　aging　(DSA)　and　yield　a　negative　strain　rate　dependence　of　the　flow　stress.　In　the　serrated　yielding　temperature　region　a　critical　transition　temperature,　T-t,　was　found.　The　critical　plastic　strain　for　the　onset　of　serrations　has　a　negative　or　positive　temperature　coefficient　within　the　temperature　region　lower　or　higher　than　T-t.　According　to　the　activation　energy,　it　is　believed　that　the　process　at　the　temperature　region　lower　than　p　T-t　is　controlled　by　the　interaction　between　Mg　solute　atom　atmosphere　and　the　moving　dislocation.　In　the　positive　coefficient　region,　however,　the　aggregation　of　Mg　atoms　and　precipitation　of　second　phase　decrease　the　effective　amount　of　Mg　atoms　in　solid　solution　and　lead　to　the　appearance　of　a　positive　temperature　coefficient　of　the　critical　plastic　strain　for　the　onset　of　serrations.　(c)　2005　Elsevier　B.V.　All　rights　reserved.