**Álvaro Gómez-Parra 1,\*, Alfredo Sanz <sup>2</sup> and Antonio J. Gámez <sup>1</sup>**


Received: 29 June 2018; Accepted: 20 July 2018; Published: 24 July 2018

**Abstract:** Turning of light alloys as aluminum-based UNS A92024-T3 is broadly implemented in the manufacture of critical aircraft parts, so ensuring a good functional performance of these pieces is essential. Moreover, operational conditions of these pieces include saline environments where corrosion processes are present. In this paper, a methodology for the evaluation of the functional performance in turned pieces is proposed. Specimens affected and not affected by corrosion are compared. In addition, performance in service through tensile stress tests of these parts is considered. The results show that turning improves the functional performance of UNS A92024-T3 alloy and that corrosion can enhance the mechanical properties of this alloy.

**Keywords:** turning; UNS A92024-T3; corrosion; surface integrity; Ra; residual stress; functional performance; ultimate tensile strength

#### **1. Introduction**

The evaluation of the performance of a manufacturing process is a complex task that can be better approached when four fundamental and complementary points of view are recognized: economical, energetic, environmental, and functional. In this context, the global process performance has been defined as the center of gravity of a tetrahedron defined by setting these four elements in its apexes [1].

In particular, the aeronautical industry considers high-performance manufacturing, even at the cost of a loss in economic performance, provided the process is enhanced from the energetic, environmental and especially, functional points of view [2–4]. Functionality can be understood as the state of health of the workpiece [5]. Therefore, the workpiece functionality is described as its ability to meet quality standards in order to fulfill the required performance in service.

For example, the critical components of an aircraft must be manufactured under high specifications of dimensional accuracy, surface finishing, and mechanical properties. In particular, the turning of aluminum alloy pieces by removing cutting fluids increases its environmental performance. This implies a loss of surface integrity that compromises safety and therefore functionality [1,6–8], as dry turning is a very aggressive process that enables tool wear or more specifically, secondary adhesion. This kind of wear involves the addition of machined material to the edge and to the rake face of the tool, giving rise to the so-called built-up edge (BUE) and built-up layer (BUL), respectively [9].

Additionally, functional properties of manufactured elements can be changed by the action of its environment. This action can be more or less intense depending on the surface state of the manufactured element. Therefore, in the case of saline environments, corrosion depends on the surface finishing of the worked elements [10] and, consequently, on the manufacturing process. In these cases, the influence of the corrosion damage on the surface properties of the workpieces must be taken into account [11]. This is the case of different structural elements of aircrafts, especially transoceanic ones. All considered, in order to approach conditions of the actual service, it is necessary to research the influence of manufacturing process on mechanicals properties in conjunction with a corrosion environment. However, to our knowledge, there are no studies in the current literature that consider the salinity effect and its relationship with the machining process and the functional performance of the workpiece. For this reason, this paper analyses the influence of turning processes in the surface integrity of UNS A92024-T3 alloys, before and after corrosion by a saline atmosphere. More specifically, the ultimate tensile strength (UTS) is measured as a reference parameter to assess the functional performance of the material under corrosion.
