Precipitation behavior of high strength high electrical conductivity Cu-Ni-Si-P alloys

Abstract

The electrical conductivity and mechanical properties of aged Cu-Ni-Si-P alloy are studied. Nine kinds of alloys with compositions, 0.5-2.0Ni, 0.1-0.4Si, 0.01-0.06P, bal. Cu, after solution treatment at 950℃ for 1 hr and then water-quenched, are aged at temperature range of 350-550℃ for 0.5-128 hrs. This alloy system has a predominant aging behavior near the 450℃, and in the standard alloy A(Cu-1.0Ni-0.2Si-0.03P), having practical usage for the Leadframe materials for semiconductor applications, strength and electrical conductivity have an optimal combination of 63% IACS and 35 Kg/$mm^2$, as aged 8 hrs at 450℃. In the alloy(A) maintaining stoichiometric ratios(Ni/Si=4.18, Ni=P=5), mechanical properties and electrical conductivity have a good combination compared with the alloys deviating stoichiometric ratios(alloy G,H,I). With a little increase of phosphorous, strength and electrical conductivity markedly enhanced due to the acceleration of forming precipitates. In the middle stage of aging treatment(1-32 hrs), the cold worked alloys have higher electrical conductivity than the no cold worked alloys. But, in the case of solution-quenched and 128hr-aged state, the cold worked alloys have lower value. By electron microscopy study, it is revealed that two kinds of precipitates, $Ni_2Si$ with orthorhombic structure and hcp $Ni_2$ P, are formed during aging. This alloy produces double aging peak when subjected to aging. It is caused by faster overaging of $Ni_2$P precipitates compared with $Ni_2Si$ precipitates. With aged 8 hrs at 450℃, the $Ni_2Si$ particles are formed in the shape of rods and needles about 100Å in size having coherency with the matrix by the relation, $<011>_{cu}//[\bar{1}00]_p//[010]_p$. And the $Ni_2P$ particles may have the shape of rod and sphere 100-200Å in size with no regular orientation in the matrix. As aged 128 hrs, both the $Ni_2Si$ and $Ni_2$ P particles are overaged. In the case of performing the cold working prior to ...