Al-Si cast aluminum alloys represented by the AlSi7Mg family (AlSi7Mg, AlSi7MgA, AlSi7Mg1A) are widely used in the manufacture of aircraft housing components. However, such components are prone to being scrapped due to defects such as porosity, wear, and corrosion during casting and service. Conventional high-energy input repair techniques, including welding and laser deposition, often induce significant thermal stress and microstructural degradation, making them unsuitable for such dimensionally sensitive components. Cold spray, as a solid-state deposition process where powder particles are accelerated to supersonic velocities and bond upon impact without melting, presents a promising low-temperature alternative. However, the application of cold spray to cast aluminum alloys faces a fundamental challenge, namely the brittle eutectic Si phases dispersed within the soft α-Al matrix tend to hinder plastic flow, contradicting the deposition mechanism that relies on severe plastic deformation. This study systematically investigates the feasibility of using this technique for the repair of AlSi7Mg alloys. The methodology involves depositing commercially available gas-atomized AlSi7MgA powder onto a grit-blasted AlSi7Mg1A substrate through a high-pressure cold spray system with industrial nitrogen as the process gas. An orthogonal experimental design is implemented to evaluate the influence of key spraying parameters-gas pressure (3, 4, and 5 MPa) and preheating temperature (400, 500, and 600 ℃) - on the coating's microstructure, porosity, microhardness, bond strength, and tensile strength. The coating is systematically characterized by optical metallography (OM), microhardness testing, tensile testing, and scanning electron microscopy (SEM). The results demonstrate that both gas pressure and temperature are crucial in determining coating quality, but temperature is found to have a more pronounced effect, with their synergistic effect leading to superior performance at higher settings. The optimal parameter combination is identified as a gas pressure of 5 MPa and a temperature of 600 ℃. Under these conditions, the powder particles undergo extensive plastic deformation, forming a highly dense and uniform coating with a porosity of less than 0.1% and an average microhardness of (116.8±6.1)HV0.1. The coating-substrate interface is clean and tightly bonded, exhibiting no discernible defects. Significantly, the adhesion strength surpasses (79.8±2.2) MPa (limited by adhesive failure in the test), and the coating's intrinsic ultimate tensile strength reaches an impressive 321 MPa. This value is not only higher than the as-cast substrate but is also comparable to the strength of AlSi7Mg1A (ZL114A) in its peak T6 heat-treated condition, as specified by national standards. This level of performance exceeds the minimum T6 strength requirements for AlSi7Mg family casting alloys in GB/T1173-2013 and reported values for nitrogen-sprayed A357/F357 coatings that rely on post-spray heat treatment. Fracture surface analysis via SEM reveals a mixed-mode failure, with both inter-particle decohesion and intra-particle ductile fracture, confirming the strong inter-particle bonding. This research conclusively proves that high-performance AlSi7MgA repair coatings, characterized by high density, exceptional bond strength, and superior tensile strength, can be fabricated using a cost-effective nitrogen-based cold spray process. This is achieved without the need for expensive helium gas or complex pre-/post-processing treatments. The findings establish a robust, economically viable, and effective technical pathway for the repair and remanufacturing of Al-Si cast aluminum alloy components, particularly within the demanding context of the aerospace industry.
Key words
AlSi7Mg /
cold-spray /
microstructure /
bonding strength /
tensile strength
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Funding
Feasibility Study on the Repair Process of Large Hydropower Station Equipment Based on Cold Spray (Z232402009)
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