Aluminum Engine Blocks Research Articles

Tribological behaviour of cast hypereutectic Al–Si–Cu alloy subjected to sliding wear

Automotive industry is seeking for weight reduction as a consequence to reduce the CO 2 emissions to the atmosphere as well as to improve engine performance. Nowadays modern aluminium engine blocks use grey iron for the cylinder bores; however, a new hypereutectic Al alloy was developed to eliminate the grey iron liners from the engine block. The main characteristic that the new alloy has to withstand is the wear resistance. The aim of the present study is to evaluate the wear performance of the new hypereutectic Al–Si–Cu alloy using a pin-on-disk tribometer. For this purpose, samples taken from a V6 aluminium engine block were tested. Metallurgical characterization was assessed using Light Optical and Scanning Electronic Microscopy. The wear evaluation was carried out at different loading conditions (10, 30, 50, 120 N), various sliding speeds (0.5, 1.0, 1.5 m/s), and various sliding distances (5, 10, 20 km), under lubricated and unlubricated conditions. Test was following ASTM G99 standard.

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.

S0304-1-2 アルミ合金製自動車エンジンブロックの残留応力測定(回折法による材料評価)

S0304-1-2 アルミ合金製自動車エンジンブロックの残留応力測定(回折法による材料評価)

Modeling of Bolt Joint Behavior of Cast Aluminum Alloy (A380-T5) by Coupling Creep and Plasticity in Finite Element Analysis

Aluminum casting alloys exhibit creep behavior when the materials are exposed to high temperature and load. In this article, the stress- and temperature-dependent creep behavior of a die casting A380-T5 aluminum alloy was simulated using a classical constitutive model. The bolt-load retention behavior of the material was analyzed in a head bolt joint in an aluminum engine under thermal cycle condition using the finite element method. In this simulation, transient thermal analysis was performed first to calculate the metal temperature at the head bolt joint as a function of time during engine thermal cycling. This temperature was then input as the thermal loading in the subsequent structural analysis to calculate its effect on the bolt-load retention. The finite element analysis (FEA) model for the bolt-load retention simulation includes not only the plasticity in all metal components but also the creep properties of head bolt threads in the cast aluminum engine block. The FEA model was validated by good correlation between the predicted head bolt-load loss and the experimental measurement during engine thermal cycling. The simulation results also indicated that creep in the head bolt threads of cast aluminum engine block was mainly responsible for the load loss in the head bolt joint.

Characterisation of an aluminium engine block

The microstructure of cast engine blocks made from an aluminium alloy was studied. Two sections of the block were selected; corresponding either to the middle or to the front end. The microstructure was evaluated at six different points in each section; two located towards the bottom of the block, within the affected by a grey iron insert, and the other four points were located in a region close to the cast-in grey iron liners. It was found that microstructural features, such as secondary arm spacing and size of silicon platelets, varied within the block.

Solidification analysis of aluminium engine block

Two V-8 engine blocks with cast-in grey iron liners were cast from a heat-treatable aluminium alloy. These blocks were instrumented by the insertion of 24 type K thermocouples placed at different points in the casting to record the thermal evolution during solidification. One of the blocks was cast after heating up the liners by induction, whereas the second was cast without the use of induction heating. The temperature–time readings from the thermocouples were obtained for thermal analysis. The solidification reactions detected were the formation of primary pre-eutectic aluminium dendrites, and two different eutectics that corresponded to Al–Si and complex Al–Si–Mg–Cu aggregates. It was found that the different solidification reactions were affected by the use of induction to heat up the liners, and by the chilling effect caused by a grey iron inset located at the bottom of the engine block moulds. The results indicate that solidification starts either at the window (bottom) or deck (top) positions in the interliners depending on whether the block was cast with or without the use of induction heating.

Design and manufacture of a carbon fiber epoxy rotating boring bar

High speed boring operations of deep holes with steel or tungsten boring bars are often hindered by the chatter vibration of boring bars because of their low dynamic stiffness and natural frequencies. The chatter is a self-excited vibration that occurs in metal cutting if, either the chip width is too large with respect to the dynamic stiffness of the system, which is proportional to the damping and static stiffness of the boring bar, or the rotating speed of the boring bar approaches one of its natural frequencies, which is proportional to the specific stiffness ( E/ ρg) of the material used. In this study, a rotating boring bar was designed and manufactured with high stiffness pitch-based carbon fiber epoxy composite to meet the requirements of boring at high rotating speed because carbon fiber epoxy composite materials have a much higher specific stiffness and higher damping than conventional boring bar materials. The optimum design parameters for the composite boring bar were experimentally determined with respect to material types and dimensions of the boring bar through vibration tests. The dynamic characteristics of the composite boring bar developed were measured by the boring operation of aluminum engine blocks. From experiments, it was found that the dynamic stiffness of the composite boring bar was about 30% higher than that of the tungsten carbide boring bar. Also, chatter did not occur up to the ratio of length to diameter ( l/ d) of 10.7, which is about a 30% improvement compared to the tungsten boring bar of l/ d of 8.0.

The role of tribo-layers on the sliding wear behavior of graphitic aluminum matrix composites

This study provides a systematic investigation of the role played by the tribo-layers that form on the contact surfaces during the sliding wear of graphitic cast aluminum matrix composites. The graphitic composites include A356 Al–10% SiC–4% Gr and A356 Al–5% Al 2O 3–3% Gr that are being developed for cylinder liner applications in cast aluminum engine blocks. Three main wear regimes, namely, ultra-mild, mild and severe wear were determined. At nearly all sliding speeds and loads in the mild wear regime a protective tribo-layer was formed. By increasing the speed and load the tribo-layer covered a larger proportion of the contact surface and became more compact and smoother. The hardness of the tribo-layers increased with the applied load and speed and reached values as high as 800 kg/mm 2. The tribo-layers were removed by extrusion process at the onset of severe wear. The topmost part of the tribo-layer consisted of iron-rich layers. The rest of the tribo-layer consisted of fractured SiC and Al 3Ni particles and thin graphite films, which were elongated over long distances in the direction of sliding, thus, reducing shear stresses transmitted to the subsurface regions. It was shown that because of the thicker and more stable tribo-layers on the contact surfaces of graphitic composites, than that of non-graphitic composites and the A356 Al alloy, the graphitic composites displayed a transition from mild-to-severe wear at load and sliding speed combinations, which were considerably higher than those of the A356 aluminum alloy and the non-graphitic A356 Al–20% SiC composite. A negative effect of the hard constituents in the tribo-layers was the scuffing damage that they inflicted on the counterface.

Tribological application of MMC for reducing engine weight

With concern increasing over environmental issues, reduction in automobile weight has become more important and has been proved to be effective for improving fuel efficiency. Metal Matrix Composites (MMC) are expected to be useful to cope with these problems. The authors have developed a new aluminium engine block which has the cylinder bore surface structure reinforced with short hybrid fibres of alumina and carbon.