Enhanced lubricity of zinc phosphate coating by stearic acid

Abstract

There is a need to reduce the friction and to prevent the galling between the galvanised steel and the shaping tools during the metal working process. Zinc phosphate (ZP) coatings are limitedly used as solid lubricant due to intrinsic high‐friction properties. This investigation explores the use of stearic acid overcoat on ZP coatings to produce surface coatings with low friction and high durability. A simple hydrothermal process was developed to fabricate ZP coatings on zinc. A stearic acid overcoat was then deposited on ZP coatings. Infrared microscopy and water contact angle measurements were used to analyse the chemical composition and the hydrophobicity of modified ZP coatings. The tribological behaviour of modified ZP coatings was evaluated by sliding against a steel ball by using a reciprocating ball‐on‐plate tribotester. Tribological results show that stearic acid overcoat on ZP coatings led to a decreased friction with greatly extended life.

Comparison of Friction Properties of GI Steel Plates with Various Surface Treatments

“…Shih tested pre-phosphated DDQ and AHSS steels by using the bending under tension test and the results showed much a lower friction coefficient compared to without the pre-phosphated coating [50]. But, in a dry condition, phosphate coatings usually do not have inherent low-friction properties and they have no practical effect on the friction coefficient [21,51]. Carlsson [31,52] evaluated the friction coefficient of organic permanent coatings by using different basic tests.…”

“…The low coefficient of friction obtained should allow for more uniform reshaping in tooling and for maximum use of the mechanical properties for sharper lines of the stampings [19,20]. The dry lubricant on the steel plates should meet the requirement of eliminating coating flaking and the need for additional oil, thus keeping the forming presses (the contact surfaces of the blank holder, punch and die) clean and ready for the next step of production [21]. A typical permanent coating consists of a coating-forming material (resin) and different types of additives (forming additives and corrosion inhibitors) [22][23][24] enhancing conductivity and/or corrosion protection [25].…”

Corrosion‐resistant and friction‐reducing performance of super‐hydrophobic coating on hot‐dip galvanised steel in a 3.5% NaCl solution

“…The zinc coating is not effective in reducing friction and preventing galling between the shaping tools and the HDGS samples. Thus, lubricating oils, emulsions, and solid lubricating films are often used to improve tribological performance 15–22 …”