Technology of Aluminium Thread forming Fasteners for Magnesium Powertrain Components Taking Weight, Corrosion and Cost Efficiency into Account - (PPT)

摘要

Thread-forming al. screws Considerable potential for reducing cost and weight. Taptite 2000 ENAW 7075 meet the rigidity requirements, in T6 condition and also in T79 condition, regarding thread-forming and generation of preload force in direct-cast core holes in AZ91, MRI153, AE44 Mg alloys. Overelastically torque of screw is possible in T79 condition. Relaxation measurement 120 hours at 120°C: greater drop in CF with ENAW 7075-T6 than with T79 / CF drop in AZ91 tendentially somewhat greater than with AE44. In galv. corrosion test: ENAW 7075 similar corrosion behaviour as EN AW 6056. Steel screw version with integral al. cup shows similar low corrosive Mg. corrosion (however, cost + weight disadvantages). In the stress crack corrosion tests: during the relevant test period the only failures in T6 condition were in combination with stainless steel frame. Since Mg components have to be joined, risk of stress crack corrosion is lower. In T79 condition the risk of stress crack corrosion is classified as non-critical. Taptite 2000 EN AW 7075 T79 thread-forming screws can be used in combination with the Mg-alloys and tightening procedures examined.