J. Talamantes-Silva

Study of residual stresses in complex aluminium castings

Abstract The working conditions within the combustion chamber of engine blocks force the use of liners able to resist the pressure and wear caused by reciprocating pistons. Most liners are made from iron alloys and can be either inserted after the block has solidified, or can be cast-in the block. Cast-in liners promote residual stresses in regions such as cylinder bridges. These stresses arise from the differences in the thermal expansion coefficient of iron and aluminium and may promote the failure of the block if high enough. This work describes the procedure followed to measure the residual stresses in aluminium engine blocks with cast-in grey iron liners by means of extensometric measurements. The trials were conducted in blocks of I-4 and V-8 configuration that were either in the as cast or heat treated condition. It was found that the stresses can be >150 MPa in tension, depending on the geometry and size of the piece. Similar analyses were carried out in blocks that have pressed-in liners, which resulted to have compressive stresses. It is concluded that these analyses can provide for an early advice when changes take place in design, processing or material.

Temperature dependent properties of heat treated aluminium alloys

The mechanical properties of different aluminium alloys used in the manufacture of power train automotive parts were studied. The alloys were cast in wedge shape ingots that promote a one-dimensional solidification gradient. Tensile samples were machined from bars that were cast with different degrees of microstructural refining and were heat treated at times and temperatures that depended on their composition. The mechanical properties were measured from samples that had been held for 200 h within the temperature range of 25 to 300°C. It was found that the increase of Cu in alloys of the Si–Mg type alloys enhanced the mechanical properties above room temperature. The best properties were found in the Al–Cu alloy.

Cast-In Hypereutectic Aluminum Liners for Engine-Blocks

A series of experimental trials was carried out to study the metallic bond produced when hypereutectic aluminum liners are cast-in hypoeutectic aluminum engine-blocks. The samples were cast in a rig that reproduces the conditions encountered during production of engine-blocks made of a type 319 aluminum alloy. The surface roughness of the liners was modified by sand blasting before casting. Some of the liners were cast after coating their surface with an amorphous carbon layer (soot) to study its effect on the metallic bond. The samples were sectioned and prepared for their examination and testing. It was found that soot does not allow the development of a metallic bond between liner and body and that the force required to remove the liners depended on such a bond; in any case, the force required to remove cast-in liners, even without bonding, was higher than that needed for removing gray iron press-in liners.