a clear change in the material's contact and plastic behavior, increasing the friction force required for adhesion and further movement. In sliding friction, increased compressive stress is proportionally equal to a rise in potential energy and temperature within the contact zone. The energy accumulation during sliding can reduce energy loss from the contact zone due to a small surface area on the surface boundary, thus, low heat conductivity. Another reason is the energy continuously forced into the metals, which is a product of acceleration and pressure. In cooperation, these mechanisms allow constant energy accumulation, causing increased energy density and temperature in the contact zone during sliding. The process and contact can be compared to cold welding or friction welding because cold welding is not truly cold, and the fusing points exhibit an increase in temperature and energy density derived from applied pressure and plastic deformation in the contact zone. Incidence and location Galling is often found between metallic surfaces where direct contact and relative motion have occurred. Sheet metal forming, thread manufacturing, and other industrial operations may include moving parts, or contact surfaces made of stainless steel, aluminium, titanium, and other metals whose natural development of an external oxide layer through passivation increases their corrosion resistance but renders them particularly susceptible to galling. In metalworking that involves cutting (primarily turning and milling), galling is often used to describe a wear phenomenon that occurs when cutting soft metal. The work material is transferred to the cutter and develops a "lump." The developed lump changes the contact behavior between the two surfaces, which usually increases adhesion, and resistance to further cutting, and, due to created vibrations, can be heard as a distinct sound. Galling often occurs with aluminium compounds and is a common cause of tool breakdown. Aluminium is a ductile metal, which means it possesses the ability for plastic flow with relative ease, presupposing a relatively consistent and significant plastic zone. High ductility and flowing material can be considered a general prerequisite for excessive material transfer and galling because frictional heating is closely linked to the structure of plastic zones around penetrating objects. Galling can occur even at relatively low loads and velocities because it is the real energy density in the system that induces a phase transition, which often leads to an increase in material transfer and higher friction. Prevention Generally, two major frictional systems affect adhesive wear or galling: