# Effect of Ti-B Grain Refiners on Wear and Corrosion of the A332 Alloy with Sr Modification
## 1 Introduction  
The A332 aluminum alloy is a hypoautectic Al-Si-Mg, which has a wide range of applications, such as common industry products in the automotive and aerospace industries, mainly due to its suitable casting properties and excellent weldability [1]. However, as-cast Al-Si alloys are composed of coarse primary face centered cubic aluminum phase dendrites and acicular-shaped eutectic phase, which lowers the mechanical properties and limits its industrial application potential [2]. Some methods can be used to solve this issue, mainly by adding elements such as Sr and Na used to modify the eutectic phase [3]. Adding Sr to molten aluminum has a metamorphic effect, which can effectively refine the eutectic phase and primary Si in the alloy, improving the mechanical properties of the alloy [4]. The effects of adding Al5 Ti1B, Al3B, and Al10 Sr in LM6 Al-Si alloy were analyzed by [PERSON] et al. [5]. The LM6 alloy was cast, and each master alloy was added individually and then tested for mechanical properties. The results show a grain size reduction and wear resistance increase with any master alloy. Moreover, the failure and mechanical properties of Al-Si casting alloys are strongly dependent on macro and microstructural features, such as size, morphology, and the distribution of primary aluminum dendrites, eutectic phase, and Fe intermetallic compounds [6]. In this sense, the Fe element, which is an impurity, is necessarily present in commercial Al alloys, as it reduces the die-casting surface flaws and increases the high temperature properties, with a better thermal stability of the alloy. However, Fe affects the mechanicalproperties, mainly caused by the precipitation of brittle intermetallic phase, Al\({}_{5}\)FeSi, that appears in morphologies such as needles or plates in the microstructure [7]. To reverse this issue, some methods have been used. Grain refiners (GR) are amongst the most efficient ones. Many advantages can be obtained from using grain refiners, such as better mechanical properties, reduced hot cracking susceptibility and better corrosion and wear resistance. The influence of grain size (d > 1 um) on yield strength (\(\sigma_{y}\)) of metals follows the Hall-Petch relationship showed in Equation (1). \[\sigma_{y}=\sigma_{o}+\mathrm{kd}^{-0.5} \tag{1}\]  
where (d) is the grain diameter, (\(\sigma_{o}\)) is the frictional stress, and (k) is a constant, generally understood as an influence of grain boundaries on strength [8]. There are several means to prepare fine-grained materials employing the most commonly used methods, i.e., friction stir processing, electrodeposition, equal-channel angular pressing, severe plastic deformation and chemical grain refinement, one of the most used in aluminum alloys [9]. The main approach to chemical grain refinement is the inoculation in the molten material with a nucleating agent. In the grain refinement of aluminum alloys, commercial ternary Al-Ti-B master alloys are added to suppress the growth of columnar grains and promote the formation of equiaxed fine-grain structures throughout the casting. The most common and commercially available ones are Al-Ti-B master alloys. For a better understanding of the grain refinement mechanism, several theories have been proposed. A substantial number of researches demonstrated that TiB\({}_{2}\) particles inoculated into Al melt via Al-Ti-B master alloys enhanced heterogeneous nucleation of primary aluminum grains. In conjunction with solute Ti atoms, this promoted the nucleation efficiency of TiB\({}_{2}\) to reach a complete wetting of TiB\({}_{2}\) particles with molten aluminum. Other particles that play an important role in the result are the soluble Al\({}_{3}\)Ti particles dispersed in the aluminum matrix. The former act as heterogeneous nucleation sites while Al\({}_{3}\)Ti particles readily dissolve in the molten material and provide solute Ti that partitions between the solid and liquid phases during solidification and, in this way, slows the growth process [10].