Automation of machining operations, being result of mass volume production of components, imposes more restrictive requirements

concerning mechanical properties of starting materials, inclusive of machinability mainly. In stage of preparation of material, the

machinability is influenced by such factors as chemical composition, structure, mechanical properties, plastic working and heat treatment,

as well as a factors present during machining operations, as machining type, cutting parameters, material and geometry of cutting tools,

stiffness of the system: workpiece – machine tool – fixture and cutting tool.

In the paper are presented investigations concerning machinability of the EN AC-AlSi9Cu3(Fe) silumin put to refining, modification and

heat treatment. As the parameter to describe starting condition of the alloy was used its tensile strength Rm. Measurement of the machining

properties of the investigated alloy was performed using a reboring method with measurement of cutting force, cutting torque and cutting

power. It has been determined an effect of the starting condition of the alloy on its machining properties in terms of the cutting power,

being indication of machinability of the investigated alloy. The best machining properties (minimal cutting power - Pc=48,3W) were

obtained for the refined alloy, without heat treatment, for which the tensile strength Rm=250 MPa. The worst machinability (maximal

cutting power Pc=89,0W) was obtained for the alloy after refining, solutioning at temperature 510 o

C for 1,5 hour and aged for 5 hours at

temperature 175 o

C. A further investigations should be connected with selection of optimal parameters of solutioning and ageing

treatments, and with their effect on the starting condition of the alloy in terms of improvement of both mechanical properties of the alloy

and its machining properties, taking into consideration obtained surface roughness.