RESIDUAL STRESS ANALYSIS AND MICROSTRUCTURE CHANGES OF HIGH STRENGTH COPPER BERYLLIUM ALLOYS AFTER ELECTRO DISCHARGE MACHINING

摘要

In the present work the influence of rough EDM parameters on the surface integrity of copper beryllium alloys is studied. The high thermal conductivity (3 to 10 times higher than steel) however requires a modification of the electro discharge machining (EDM) parameters compared to the well-known parameters for steels. Phase changes, residual stress and micro-hardness profiles in depth are analysed and interpreted. The copper beryllium alloy used in this study has the chemical composition of 1.9wt% Be, 0.25wt% Co+Ni and copper. Micro-hardness as well as residual stress depth profiles can be related to the beryllium diffusion between α and γ copper phases and consequent microstructure changes. The maximum and minimum of micro-hardness and residual stress values are independent of the discharge energy. The depth, where the maximum value of the residual stress occurs, increases with the discharge energy. The maximum values of micro-hardness and residual stress observed are 450HV and 400MPa, respectively. The thickness of the white layer and the heat affected zone decrease when the discharge energy is reduced.