420 MPa coating steel for automobile beam and production method thereof

420 MPa coating steel for an automobile beam comprises, by weight, 0.06%-0.09% of C, 0.025% or less of Si, 0.80%-1.00% of Mn, 0.015% or less of P, 0.008% or less of S, 0.020%-0.060% of Als, and 0.015%-0.025% of Nb. A production method comprises the steps that all the raw materials enter a converter to be smelted and then enter an argon station for argon blowing; steel is tapped and subjected to continuous casting to form blanks, and the casting blanks are heated; segmented hot rolling is conducted; laminar cooling is conducted at a variable speed; reeling is conducted; and finishing and subsequent processes are carried out. According to the 420 MPa coating steel for the automobile beam and the production method thereof, under the design of low alloy components, variable speed cooling and segmented cooling are adopted, on the premise of guaranteeing the mechanical property of a steel plate, the produced beam steel for coating has excellent surface quality and platability, the steel can be directly used for hot galvanizing production, and the surface of the steel plate is exquisite and durable.