Properties of free machining aluminium alloys at elevated temperatures

Abstract

During laboratory tests of machinability performed in the course of development of new free-cutting alloys, it was found that the temperature of material being dry machined can reach values as high as 350 °C or more in areas close to cutting tool. During machining it is therefore theoretically possible that in some cases, such as failure of cutting fluid inflow, the temperature of thin wall machined piece may exceed normal temperature considerably. In modern methods of machining using high cutting rates the material may undergo impact loads at elevated temperatures. This type of load can be simulated using the impact bend test, so called Charpy impact test according to European standard EN 10 045-1. Unlike common construction AA6082 alloy, the free machining AA6262 and AA6023 aluminium alloys show a significant decrease in notch impact strength KU at elevated temperatures. This drop of KU, caused by melting of disperse phases containing low-melting metals, takes place within a certain relatively narrow transition range of temperature. This decrease in notch impact strength leads to the risk of occasional fracture of parts manufactured from these alloys by cutting process.