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Critical for the use of aluminum alloys for cylinder heads are strength and durability. In our study, the mechanism of the low cycle fatigue and creep was clarified based on the mechanical properties of aluminum alloys, such as tensile, compressive, thermal fatigue and creep characteristics, which were determined by conducting tests on test pieces. The behavior of a cylinder head under cyclic thermal condition was represented by using a high-precision analysis method with cyclic creep taken into consideration. Moreover, the high-precision analysis method turned out to be effective in estimating a low cycle fatigue life under the cyclic thermal condition.

There is ever an increasing need for weight reduction and high performance of engine (clean smoke and improving fuel economy) To achieve this, recently aluminum castings are used for engine parts such as cylinder heads that construct combustion chamber and are required thermal resistance. This paper describes thermal fatigue tests of aluminum castings that are made under various conditions of cooling rate during solidification, heat treatment, and chemical compositions. It further investigates the influence of material (such as cooling rate, chemical conmposition and heat treatment) and mechanical properties (such as σB, δ, E ) on thermal fatigue life of aluminum castings.

There are many methods for case hardening such as conventional induction hardening and newly developed electron beam hardening. Electron beam hardening has been adopted in Isuzu and the reliability of engines has been improved. The beam power of the electron beam hardening equipment used was 6 kW. Various conditions of electron beam were scanned across specimens (SCM435H) in order to investigate the influence on hardening properties. As a result, relation between case depth and beam current and relation between case depth and beam scanning time were confirmed. And when the depth exceeded 1 mm, there were cracks in surface melted area. Electron beam hardening was applied to tappets according to the above fundamental experiments, and uniformly hardened layers were obtained. Durability of engines with electron beam hardened tappets was improved twice as much as those with non-hardened tappets.