Alternatives to hard chromium plating on piston rods

As a main part of hydraulic cylinder, the piston rod is used in tough surrounding and corrosive condition; consequently a high quality protecting layer is essential. Currently EHC, electroplating hard chromium (hard chrome) is a widespread method for piston rod due to powerful performance and low cost. Unfortunately the plating process contains hexavalent chromium (Cr) which is toxic and carcinogenic; perhaps it will be prohibited in the nearing future. Therefore it is crucial to seeking alternatives to hard chrome for piston rod manufacturer. Through extensive searching for alternatives to hard chrome, the competitors like HVOF, electroplating tungsten plating and stainless steel linear were studied in the present work. Since microhardness and corrosion resistance are top priorities, after comparison perhaps Cr3C2-NiCr20% HVOF is the most promising technique. Distinct pretreatments Cr3C2-NiCr coatings were compared with hard chrome in pendulum impact test, hardness test and acetic acid salt spray (AASS) test. The results indicate that hard chrome show higher toughness more than 40% compare with HVOF, the microhardness of HVOF is higher than hard chrome, mean value 1784 Vs. 1244 HV and both coatings have excellent bonding strength. After 40 hours in AASS test, the hard chrome was rated No. 10, however the HVOF just No. 6.