Processes for welding composite materials and articles therefrom
The invention is directed at a method for welding a composite material and to welded structures thus prepared. The method includes a step of contacting a substrate material with a composite material, wherein the composite material includes a pair of spaced apart steel sheets and a core layer between the sheets; the volume of the core layer is about 25 volume % or more, based on the total volume of the composite material; the core layer includes a plurality of steel fibers arranged in one or more masses of fibers that extend the thickness of the core layer so that the core layer is in electrical communication with the steel sheets; and the steel fibers have a cross sectional area perpendicular to the length of the fibers from about 1×10 −5 mm 2 to about 2.5×10 −2 mm 2 .
1. A process of forming a weld joint comprising the steps of:
providing a substrate material, wherein the substrate material is a metallic material;
providing a light weight composite material;
placing the substrate material in contact with the light weight composite material to form a weld stack, and
welding the light weight composite material directly to the substrate material; wherein the step of welding includes a step of applying a weld current from about 2.5 kA to about 25 kA to the substrate material and the light weight composite material using electrodes of a resistance welding apparatus to weld the substrate material with the light weight composite material so that a weld is achieved characterized by a weld button having an area of about 1 mm 2 or more;
wherein the light weight composite material includes a pair of spaced apart steel sheets having an area of overlap and a distance between the steel sheets, and a core layer having a thickness; wherein the light weight composite material includes a space between the pair of spaced apart steel sheets having a volume defined by the area of overlap and the distance between the steel sheets, wherein the core layer is in the space between the steel sheets;
the core layer is present at a concentration from about 25 to about 95 volume percent, based on the total volume of the light weight composite material;
the total volume of the steel sheets of the light weight composite material is from about 5% to about 75%, based on the total volume of the light weight composite material;
the core layer includes a polymeric matrix and a plurality of steel fibers arranged in one or more masses of fibers that extend the thickness of the core layer so that the core layer is in electrical communication with the steel sheets, wherein less than 40% of the steel fibers span individually the thickness of the core layer; and
the steel fibers have a length of about 200 μm or more and less than 7 mm;
the steel fibers have a cross-section perpendicular to the length of the steel fibers having a cross-sectional area from about 1×10 −5 mm 2 to about 2.5×10 −2 mm 2 , and the cross-section perpendicular to the length of the steel fibers has a width, a thickness, and one or more straight sides;
wherein the polymeric matrix includes one or more polymers and the core layer has a volume ratio of the polymer to the steel fibers that is greater than 2.5:1, the steel fibers are present at a concentration greater than about 10 percent by volume, based on the total volume of the core layer of the light weight composite material; and the core layer fills at least about 90 volume percent of the space between the pair of spaced apart steel sheets; the one or more polymers includes a polyolefin;
the core layer is free of voids and pores,
wherein the light weight composite material has a stamped configuration.