Effect of Dendrite Arm Spacing on Mechanical Properties of Aluminum Alloy Cylinder Heads and Engine Blocks 2005-01-1683

In our previous work we studied the factors that affect dendrite arm spacing of cylinder heads in various aluminum alloys. The present paper will be focused on mechanical properties of cylinder heads and engine blocks of aluminum alloys with different dendrite arm spacing.

Before evaluating the DAS effect on mechanical properties, some factors have been taken into account such as the response of mechanical properties to aging of different production castings having different DAS, and the influence of dimension and weight of real products on the heat treatment and mechanical properties. Comparisons were done among various production castings with the same alloy composition (in particular the Fe content), the same modification grade and similar percentage and size of porosity Furthermore, specimens were cut from different castings with the same alloy, then the same heat treatment cycle was performed on dissected specimens instead of the whole cylinder head or engine block, in order to avoid the interference of dimension and weight of real castings.

The results on the production castings of A356 alloy with a T6 heat treatment condition show that the UTS and percent elongation were increased in a great extent with reducing in DAS, while the yield strength was found to remain unaffected by DAS. For different cylinder heads in 319 alloy without heat treatment and cooled naturally in air both UTS and YS were found to decrease with increasing DAS, but elongation and HB remained constant as DAS increased from 20 to 30 μm. In heat treatment conditions of cylinder heads and engine blocks in 319 alloy, castings with lower DAS have higher tensile properties in the range of aging temperature from 150°C to 230°C. The study on production castings with a peak-age T6 heat treatment shows that both ultimate tensile strength and yield strength were increased as DAS decreased.