Heat Treatment of Cold-Sprayed C355 Al for Repair: Microstructure and Mechanical Properties

Abstract

Cold gas dynamic spraying of commercially pure aluminum is widely used for dimensional repair in the aerospace sector as it is capable of producing oxide-free deposits of hundreds of micrometer thickness with strong bonding to the substrate, based on adhesive pull-off tests, and often with enhanced hardness compared to the powder prior to spraying. There is significant interest in extending this application to structural, load-bearing repairs. Particularly, in the case of high-strength aluminum alloys, cold spray deposits can exhibit high levels of porosity and microcracks, leading to mechanical properties that are inadequate for most load-bearing applications. Here, heat treatment was investigated as a potential means of improving the properties of cold-sprayed coatings from Al alloy C355. Coatings produced with process conditions of 500°C and 60 bar were heat-treated at 175, 200, 225, 250°C for 4 h in air, and the evolution of the microstructure and microhardness was analyzed. Heat treatment at 225 and 250°C revealed a decreased porosity (* 0.14% and 0.02%, respectively) with the former yielding slightly reduced hardness (105 versus 130 HV 0.05 as-sprayed). Compressive residual stress levels were approximately halved at all depths into the coating after heat treatment, and tensile testing showed an improvement in ductility.

Yenilikçi Ürün Tasarımında Fonksiyon Analizi ve Budama Yöntemi

“…Buna ek olarak soğuk püskürtme, sünekliği çok düşük olan kaplamalar oluşturur, çünkü yoğun plastik deformasyon sonucu yapı çok sertleşebilir ve parçacıklar arası bağlar nispeten zayıf olabilir [26,27]. Kaplama işlemi sonrasında yapılan ısıl işlemler ile çekme mukavemetinin ve sünekliğin arttığı belirlenmiştir [28]. Aşınma, göreceli hareket esnasında yüzeyde meydana gelen malzeme kaybı olup düşük, orta ve şiddetli olmak üzere 3 farklı rejimde sınıflandırılmaktadır [56].…”

Heat Treatment Influence on Mechanical Properties of Nickel Based Cold Spray

“…The above properties predetermine CS as a potential method for repairing components by replacing or refilling flawed material. However, it is necessary to determine the material properties of applied CS [3][4][5] and to prove the applicability. According to previous experience in Centrum Vyzkumu Rez (CVR), CS coatings (few millimetre thickness) exhibits sufficient strength and compactness to be tested separately without the substrate.…”

“…As-sprayed CS coatings are normally characterized by high strength and low ductility [3], which lead to deterioration of fracture properties. Heat treatment (HT) can improve CS ductility for certain materials [4,5]. Hereafter, one of the determined goals is to obtain suitable CS coating, which can be used to repair certain pipe-components in power industry.…”

Material Properties of Nickel Based Cold Spray by Means of Small Specimens

“…CS has a potential due to the above properties to be a method for replacing or refilling flawed material with aim to repairing components. Nevertheless, the material properties of applied CS has to be determined [3][4][5] and the applicability of the layer has to be proven. CS coatings (few millimeter thickness) exhibits sufficient strength and compactness to be tested separately without the substrate as shown by experience in Centrum Vyzkumu Rez (CVR) and will be discussed further in the paper.…”