Influence of Two Hexavalent Chromium-Free Coating types on Mechanical Behavior of Bolted Joints

The goal of this work is to evaluate the performance of two different coating technologies for bolts. They are based on zinc and aluminum with no hexavalent chromium in their composition. These technologies were implemented because international laws for environmental and human health protection are limiting the use of the hexavalent form of chromium because it causes different cancer types in workers, mainly in recycling processes. The experimental tests were performed using M12x1.25–10.9 bolts that were submitted to the test of torsion-tension. The clamping load, total torque, torque on thread, torque on the bolt head, and twist angle were measured. The friction coefficients between the nut and bolt threads, between the face of the nut and its bearing surface, the global coefficients of friction, and the nut factor were also measured and analyzed.