DC (Direct Chill) Casting

A continuous method of making ingots or billets for sheet or extrusion by pouring the metal into a short mold. The base of the mold is a platform that is gradually lowered while the metal solidifies, the frozen shell of metal acting as a retainer for the liquid metal below the wall of the mold. The ingot is usually cooled by the impingement of water directly on the mold or on the walls of the solid metal as it is lowered. The length of the ingot is limited by the depth to which the platform can be lowered; therefore, it is often called semicontinuous casting.

Dead Flat

Perfectly flat. As pertaining to sheet, strip or plate. Refer to Stretcher Leveling.

Deburring

A method whereby the raw slit edge of metal is removed by rolling or filing.

Decoration (of dislocations)

Segregation of solute atoms to the line of a dislocation in a crystal.

Deep Drawing

The process of cold working or drawing sheet or strip metal blanks by means of dies on a press into shapes which are usually more or less cup-like in character involving considerable plastic deformation of the metal. Deep-drawing quality sheet or strip steel, ordered or sold on the basis of suitability for deep-drawing.

Defect

A defect is anything that renders the aluminum unfit for the specific use for which it was ordered.

Dendrite

(1) A crystal that has grown in treelike branching mode. (2) A crystal that has a tree-like branching pattern, being most evident in cast metals slowly cooled through the solidification range.

Dendritic Segregation

Inhomogeneous distribution of alloying elements through the arms of dendrites.

Dent

(1) For rolled products, a sharply defined surface impression on the metal which may be caused by a blow from another object. (2) For extrusions, a synonym for handling mark. See "Mark, Handling".

Dent, Expansion

Localized surface deviation from flat generated by expansion of vapor during thermal treatment of cold rolled coiled sheet.

Dent, Repeating

Repeating depression caused by a particle adhering to a rotating roll over which the metal has passed.

Die Sinking

Forming or machining a depressed pattern in a die.

Die-Lines

Lines of markings caused on drawn or extruded products by minor imperfections in the surface of the die.

Diffusion

(1) Spreading of a constituent in a gas, liquid or solid, tending to make the composition of all parts uniform. (2) The spontaneous movement of atoms or molecules to new sites within a material.

Dish

A concave surface departing from a straight line edge to edge. Indicates transverse or across the width.

Diffusion Streak

Surface streaks on an alclad or a clad sheet resulting from alloying constituents diffusing from the core into the cladding during thermal treatment.

Dirt

Foreign debris from rolling or post-rolling operations imbedded in or under the coating.

Disc

A circular blank fabricated from plate, sheet or foil from which a central concentric area has been removed.

Dislocation

A linear defect in the structure of a crystal.

Double Shear Notch

An abrupt deviation from straight on a sheared edge. This offset may occur if the flat sheet or plate product is longer than the blade for the final shearing operation.

Drawing

(1) Forming recessed parts by forcing the plastic flow of metal in dies. (2) Reducing the cross section of wire or tubing by pulling it through a die. (3) A misnomer for tempering.

Drawn-In Scratch

A scratch occurring during the fabricating process and subsequently drawn over making it relatively smooth to the touch.

Drawn Product

A product formed by pulling material through a die.

Drawn Shape

A shape brought to final dimensions by drawing through a die.

Dry Sheet

Lube, Low:

Dry Surface

A foil surface substantially free from oily film, and suitable for lacquering, printing or coating with water-dispersed adhesives.

Ductile Crack Propagation

Slow crack propagation that is accompanied by noticeable plastic deformation and requires energy to be supplied from outside the body.

Ductility

(1) The ability of a material to deform plastically without fracturing, being measured by elongation or reduction of area in a tensile test, by height of cupping in an Erichsen test or by other means. (2) The capacity of a material to deform plastically without fracturing. (3) The property of metals that enables them to be mechanically deformed when cold, without fracture. In steel, ductility is usually measured by elongation and reduction of area as determined in a tensile test.

Duct Sheet

Coiled or flat sheet in specific tempers, widths, and thicknesses, suitable for duct applications.

Duralumin (obsolete)

The trade name applied to the first aluminum-copper-magnesium type of age-hardenable alloy (17S), which contains nominally 4% Cu, 1/2% Mg. The term is sometimes used to include the class of wrought aluminum-copper-magnesium alloys that harden during aging at room temperature.