Effects of heat treatment on the electrical conductivity hardness and microstructure evolution of Cu-3.0Ni-0.75Si-0.3Co alloy were investigated

and the strengthening mechanism of the alloy was described.The results show that the amounts of Ni3Si2 and CoSi phase particle in the grain and grain boundary of Cu-3.0Ni-0.75Si-0.3Co alloy are decreased and the super-saturation solid solubility is increased with the increase of the solution temperature by SEM（scanning electron microscopy）observation.As a result of minor second phase particle with smaller sizes in the microstructure

the second phase particles cannot be observed on the SEM pictures by XRD after 950 ℃×1hsolid solution treatment

which reveal that solute elements are sufficiently dissolved into copper matrix.The aging treatment is conducted at different temperatures after 950℃×1hsolid solution treatment and cold rolling of60% deformation ratios.The results show that the electrical conductivity is increased rapidly at firstly and then tends to be flattened with the increase of the aging time.The electrical conductivity is increased continuously with the increase of the aging temperature.And the hardness is increased at firstly and then decreased with the increase of the aging time.And with the increase of ageing temperature

time reaching hardness peak is shortened.The desirable comprehensive properties can be obtained at 950℃×1hsolid solution treatment

60% cold rolling and 450 ℃×6haging treatment

where hardness and electrical conductivity reach 257 HB and 20.18 MS/m

respectively.