Crack Initiation Mechanism in Casting AC4B Aluminum Alloy Parts with Complex Structure

Wanqing Deng,Dingfei Zhang,Qingwei Dai,Songzhu Zhu,Daliang Yu,Wen Yang

doi:10.3390/met11010097

Wanqing Deng, Dingfei Zhang + Show 4 more

Open Access

https://doi.org/10.3390/met11010097

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Abstract

Hot tears were frequently formed in Aluminum (Al) parts with complex structure. In this study, OM (optical microscope), SEM (scanning electron microscope), EDS (energy dispersive spectrometer), and FDM (finite difference method) were used to reveal the hot tears mechanisms in the casted AC4B Al engine. Shrinkage porosities with the size of 300–500 μm were found in casted specimens near the parts’ surface. Many cracked brittle Fe-bearing phase were also found in crack section. The secondary dendrite arm spacing observation in five typical positions showed that the cooling rate in position 5 was faster than that in position 1. The impropriety solidification sequence in position 5 and position 1 impeded the solidification feeding of position 1, and it might lead to casting defects or even casting cracks. Numerical simulation also showed that solidification sequence promoted casting defects, which was accordant with microstructure observation. Impurity may concentrate at position 5 during filling. It is concluded that large β-Fe intermetallics and improper solidification sequence together contributed to crack initiation in the engine.

Highlights

Microscope microstructure of casted andcracks quenched frequently found in position
Secondary arm spacing in AC4B casting components
Little wasconclusions detected in have the casting defects with the size of 300–500 μm that can only be found near the surface of the components

Summary

Introduction

Al-Si-Cu series cast alloys were widely used as engine and engine blocks in the automotive industry for its good castability and excellent mechanical properties in ambient and elevated temperature [3,4]. The service performance of cast Al alloys components can be affected by many factors, such as alloying elements, casting methods, technological parameters, and so on [5,6,7]. Casting defects, such as hot tearing, embrittling secondary phases, porosity, and solidification shrinkage frequently cause performance deterioration in applications [8].

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