Preload relaxation of steel fasteners in ACuZinc alloy sand-castings
of two ACuZinc (Al-Cu-Zn) alloys, i.e. ACuZinc5 and ACuZinc 10 at a constant temperature of 80, 100 and120°Cwas continuously monitored. The equipment used for these tests consists of a calibrated load cell, an oil-bath, and a data-acquisition system. The load cell is used to monitor the preload loss in ISO M6 x 1 steel screws set into sand-castings made from alloys ACuZinc5 and ACuZinc 10, and tightened to produce an initial preload of 6 kN. The oil-bath is used to heat and maintain the required test temperature throughout the experiment. All tests were conducted in duplicate for periods of up to about 160 hours. The data-acquisition system is used to record the load-relaxation data continuously for the whole test period.The results showed that for both alloys, the initial preload loss was rapid, followed by an approximately logrithmic decay, with no lower limit. ACuZinc 10 had better resistance to load loss than ACuZinc5 under all testing conditions. Both ACuZinc alloys were found superior than zinc alloys No.3, No.5 and No.2 for load-relaxation strength, due to the higher copper contents which contribute greatly to their resistance to load loss in the form of second-phase (e) particles.