Aluminum and stainless steel handles to compare
Stainless steel suits a framelock, where the handle doubles as the lock, and aluminum suits a buyer who wants anodized color. Buck says a frame lock's "locking mechanism is a section of the handle," and Böker says framelock scales are usually particularly hard metals, stainless steel among them; Kershaw says anodizing enables it to add color to its aluminum handles.
By Buck's and Kershaw's descriptions, a framelock puts the handle to work in the mechanism. Buck says a frame lock "functions like a liner lock," and Kershaw says the metal side of the frame, the lockbar, "butts up against the backend of the blade (the tang)" when the knife is open. Böker says framelock scales are usually hard metals such as stainless steel "because these materials offer adequate resistance to the blade when the knife is used." The lock bar has an entry of its own.
By World Stainless's definition, the steel in a stainless steel handle carries a minimum of 10.5 percent chromium by mass. Rust is a separate question, answered in whether stainless steel ever rusts.
Kershaw adds color to aluminum handles by anodizing. Kershaw says "Anodizing makes aluminum even stronger and enables Kershaw to add scratch and fade resistant color to knife handles," and Böker describes anodizing as oxidizing a metal surface with an electrochemical process. Böker calls aluminum itself "a soft and tough metal" that is "very light and at the same time has a high strength." The aluminum handle entry treats the metal in general, and caring for an aluminum handle walks through day to day upkeep.
On stainless, the spec pages for Kershaw's retired Norad and Esteem list a bead-blasted finish, a surface explained in the bead blast finish entry. Kershaw says the coatings and finishes on its "blades (and metal handles)" give "some protection against scratches, wear, and corrosion of the metal surface."
Published densities compare the two metals, one alloy each. Kaiser Aluminum lists its 6061 alloy at a nominal density of 0.098 pounds per cubic inch and Carpenter Technology lists its 410 stainless at 0.2800 pounds per cubic inch, so on those figures the aluminum has about 35 percent of the stainless steel's density. Neither figure describes a particular knife, and a product page's Weight row is the distributor's shipping weight, packaging included.