Cast-In Cylinder Liners Designs to Improve Bonding and Shear Strength for Aluminum Block

摘要

The tendency to use aluminum alloys to replace conventional gray cast irons (GCI) materials in engine blocks of passenger cars is gaining more and more importance driven by reduction of engine weight to achieve expectation for lowering fuel consumption and CO_2 emissions. Cast-in cylinder liners are commonly applied inside of aluminum engine blocks with designs of the outer surface usually selected through analysis of the aluminum casting process (e.g., high pressure die casting, precision sand cast), geometry complexity, thermal and mechanical loads. A good quality of clamping (bonding and shear strength) between the cast-in cylinder liner and aluminum block might guarantee a reliable heat transfer and thus low bore distortion. The good clamping can also contribute to improve the final machining of the liner after block casting. The most effective variants of cast-in cylinder liner designs were selected for the evaluation of clamping performance. The variants were based on conventional thread turned, threaded with addition of undercuts profile, and two designs based on as-cast rough surface with different roughness depth (0.62 and 1.26 mm). The results showed that the as-cast rough surface with roughness depth of 1.26 mm reached maximum values for bonding strength (30 MPa) and shear strength (98 MPa) due to better penetration of the melted aluminum into the rough volume surface. The threaded with addition of undercuts profile design also meets higher targets in the bonding (22.7 MPa) and shear strength (37 MPa) when compared to conventional machined liners. The good clamping performance added with freedom of outer diameter that enable different shapes in connection with tighter tolerance, places this design as promising technology for modern aluminum engine blocks with low inter-bore distance.