The invention relates to a hollow variable-
diameter porous friction head and a preparation method for a surface
composite material of a
metal material, particularly relates to the
friction stir welding friction head and a
welding method, and solves the problem that for preparation of a
metal matrix
composite material, an enhanced phase is distributed unevenly because particles are splashed and translated in a material
processing process caused by the fact that the enhanced phase is needed to be placed in a material to be processed. A
welding tool comprises an upper cylinder body and a lower cylinder body which are vertically arranged and made into a whole, the upper cylinder body and the lower cylinder body are provided with an upper hole channel and a middle hole channel respectively along axes, four horizontal through holes are all communicated with the middle hole channel, each horizontal through hole is communicated with two lower vertical hole channels, a variable-
diameter sheet is arranged at the bottom of the upper hole channel, and the inner
diameter of a variable-diameter hole is less than the inner diameter of the middle hole channel. The method includes: 1 determining geometric dimension of the friction head; 2 adding enhanced-phase particles; 3 adjusting a
slant angle of the friction head; and 4 performing the
friction stir processing on the surface of a workpiece to be processed, and achieving preparation of one surface
composite material. The hollow variable-diameter porous friction head and the preparation method for the surface composite material of the
metal material are used for preparation of surface composite material
layers of the metal material.