Effect of Microstructure on High Temperature Mechanical Properties of A319 Casting Alloy for Automotive Cylinder Heads

Abstract

A quantitative study has been conducted to evaluate the relationship between microstructural features such as secondary DAS (dendrite arm spacing), eutectic structures and the mechanical behaviors of A319 casting alloys. Depending on the cooling rate affecting the primary and eutectic microstructure, the storage elastic modulus measured by DMA (dynamic mechanical analysis) increased with decreasing DAS, with a concomitant increase in the tensile strength and elongation at RT and also high tempertures. Contrarily, the thermal expansion coef cient increased with increasing temperature, but did not vary with microstructural changes. The hardness of the eutectic phase increased with increasing DAS due to the enlarged size of the eutectic particles, whereas the hardness of the primary phase was similar regardless of DAS, owing to the precipitates that formed during heat treatment. The increase of both of LCF (low cycle fatigue) and HCF (high cycle fatigue) lives with decreasing DAS was observed, mainly due to homogeneous deformation owing to the ne size of eutectic silicon and Fe intermetallic particles. The results of fractography observation showed that ner α-Al and eutectic phases were effective to the resistance of fatigue crack initiation and propagation due to the shorter crack path along the secondary particles. The LCF lives increased with increasing test temperature according to the Cof n-Manson relation due to the larger elongation. On the other hand, an analysis of the fatigue lives with the hysteresis loop energy, which consists of both strength and elongation, showed that the fatigue lives were normalized with an alloy of the same strengthening mechanisms regardless of the test temperature. DMA analysis demonstrated that the mechanical properties of the Al 2 Cu precipitate hardened alloy were maintained at temperatures greater than 250 C, whereas degradation in the mechanical properties of the Mg-containing alloy occurred at 170 C due to coarsening in the precipitation phase of Mg 2 Si.

Effect of Heat-Treating on Microstructure and High Cycle Bending Fatigue Behavior of AZ91 and AZE911 Magnesium Alloys

“…where σ a is stress amplitude, N f is fatigue lifetime, σ f ′ is the fatigue strength coefficient, and b stands for the fatigue , Nd [4], MM [28], and RE, (e) the HCF behavior of AZ91-T6 versus A319-T6 [29], and (f ) the HCF behavior of AZE911-T6 versus A356-T6 [25] and A380-T6 [26].…”

“…Figure 4: (a) All data, (b) averaged values, after and before heat treatment, and (c) the HCF behavior of AZ91-T6 in this research versus other research [7,9,16-18,20], (d) the HCF behavior of AZE911-T6 versus AZ91 containing rare earth Ce[27], Nd[4], MM[28], and RE, (e) the HCF behavior of AZ91-T6 versus A319-T6[29], and (f ) the HCF behavior of AZE911-T6 versus A356-T6[25] and A380-T6[26].…”

Ca-modified Al–Mg–Sc alloy with high strength at elevated temperatures due to a hierarchical microstructure

“…The UTS, YS and specific strength of the current alloy are also compared with the values for conventional and commercial heat-resisting aluminum alloys, i.e., A356, A319 and M124, as shown in Fig. 8d-f, respectively [42][43][44][45][46][47]. Compared with A356 and A319 alloys, the UTS of Ca-modified alloy in aging states is lower at room temperature and 150 °C, but better at 250 °C and higher temperatures, and even higher than that of M124 at 300 °C.…”