Abstract: A process for coating a preform with a flux is provided, which comprises: preform pretreatment, powder preparation, coating, curing, and post treatment. The process has the advantages of uniform and stable coating, highly controllable coating thickness, strong binding force, being efficient and environmentally friendly, and low cost, thus being suitable for coating the surface of various preforms with a flux.

Abstract: The present invention provides a high-concentration flux for being sprayed on a preform. The flux has a composition comprising, based on weight percent, 35-50% of a film-forming agent, 1-20% of an active substance, 0.1-1.5% of a surfactant, and 0.005-0.02% of a dye, with the balance being a solvent. The flux has the advantages of excellent coating performance, highly controllable coating amount, high activity, and low active substance residue after welding, and is suitable for the efficient spraying process and highly reliable welding of various preforms.