Failure Analysis of an Aluminum Component During Crimping Operation

Aluminum alloys are widely used in the manufacturing industry due to their excellent strength-to-weight ratio, corrosion resistance, and castability. However, when not properly heat-treated or when subjected to localized stresses, they can fail prematurely. This article summarizes a laboratory failure analysis conducted on aluminum samples that fractured during a crimping operation at pressures ranging from 1,250 to 1,300 psi.

1. Background

Three aluminum samples were submitted for analysis following failure during a high-pressure crimping process. The main goal of the investigation was to identify the root cause of failure and determine whether material quality, microstructure, or manufacturing parameters contributed to the issue.

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2. Chemical Analysis

Optical emission spectroscopy (OES) revealed that the alloy corresponds to a hypoeutectic Al–Si casting composition, specifically an A356-type aluminum alloy. The material contained approximately 7% silicon, along with trace levels of magnesium, titanium, and iron. These findings align with typical casting grades used for automotive and electrical applications.

While the chemical composition was within specification, the microstructural characteristics suggested that no solution heat treatment or artificial aging had been performed — a crucial step in achieving the mechanical properties expected of A356 alloys.

3. Microhardness Results

Microhardness testing confirmed an average value of 65.98 HV1 across all test points. This uniform hardness is consistent with an as-cast condition rather than a heat-treated one. For comparison, solution-treated and aged A356 aluminum typically reaches hardness levels of 95–110 HV1, whereas as-cast material falls between 55–75 HV1.

4. Microstructural Examination

Optical microscopy revealed coarse primary aluminum dendrites surrounded by a continuous eutectic silicon network. The dark silicon-rich regions indicated the absence of spheroidization — a direct consequence of the missing heat treatment. Such unrefined microstructures result in reduced ductility and a higher tendency for brittle fracture.

Stereo microscope analysis further revealed distinct cleavage-like fracture surfaces, with faceted and granular textures characteristic of brittle fracture. River patterns radiating from crack initiation sites confirmed rapid crack propagation under localized stress.

5. Failure Mechanism

The failure was caused by localized stress concentration in the as-cast aluminum structure. Crack initiation occurred at interdendritic silicon regions, which are inherently brittle. Without heat treatment to homogenize the silicon phase, these areas acted as weak points. When the crimping force was applied, cracks propagated quickly with minimal plastic deformation — leading to a brittle, cleavage-like fracture surface.

In short, the component failed due to the combined effects of stress concentration and a brittle, unrefined microstructure.

6. Recommendations

  1. Apply Proper Heat Treatment: Perform solution heat treatment followed by artificial aging to improve ductility and toughness.
  2. Optimize Casting Parameters: Reduce cooling rate variations to achieve finer dendritic spacing and minimize porosity.
  3. Implement Quality Inspection: Regularly perform microstructural and hardness checks to ensure desired mechanical properties.
  4. Design Review: Reassess the crimping tool geometry to minimize stress concentration points.

7. Conclusion

This failure analysis underscores the importance of post-casting heat treatment in aluminum alloys such as A356. Although the chemical composition met standard requirements, the coarse, brittle microstructure and absence of solution and aging treatments rendered the material vulnerable to fracture under applied load. Through improved processing and inspection practices, such premature failures can be effectively prevented.