Yaşlanabilir alüminyum alaşımlarının aşınma davranışları /

Abstract

Bu çalışmada; Al-Si-Cu döküm ve Al-Mg-Si dövme alaşımlarına uygulanan ısıl ve/veya soğuk işlemlerin, alaşımların aşınma davranışları üzerindeki etkileri incelenmiştir, Al-Mg-Si alaşımı %16 soğuk işlem uygulanarak sertleştirilmiştir. Al- Si-Cu ve Al-Mg-Si alaşımlarına uygulanan ısıl işlem, 525°C de 7 saat süreyle solüsyona alma, akabinde su verme ve 175°C de 16 saat süreyle yaşlandırma aşamalarını kapsamaktadır. Buna ilave olarak Al- Mg-Si alaşımına solüsyona alma işleminden sonra %16 düzeyinde soğuk işlem uygulanıp yaşlandırılmıştır. Yapılan deneyler sonucunda yaşlandırma işlemi ile iletkenlik değerlerinin arttığı gözlenmiştir. En yüksek iletkenlik değeri solüsyona alma+soğuk işlem +yaşlandırma uygulanmış Al-Mg-Si alaşımında elde edilmiştir. Aynı şekilde yaşlandırma işlemi İle birlikte sertlik ve mukavemet değerleri de artmıştır. Metal-Abrasiv deneyleri sonucu, soğuk işlemin aşınma direnci üzerinde etkisi olmadığı görülmüştür ve en iyi aşınma direncinin solüsyona alma+soğuk işlem+yaşlandırma uygulanmış Al-Mg-Si alaşımında elde edilmiştir. Bu işlem aşınma direncini %30 düzeyinde arttırmıştır. Metal-Metal aşınma deneyleri sonucu ise, solüsyona alma+soğuk işlem+yaşlandırma uygulanmış Al-Mg-Si alaşımının aşınma direncini %40 düzeyinde arttırdığı saptanmıştır

Aluminium is a high weight metal, with a density of 2.70 gr/cm3 or one-third the density of steel. Although aluminium alloys have relatively low tensile properties compared to steel, their strength-to- weight ratio, as defined below, is excellent. Aluminium is often used when weight is an important factor, as in aircraft and automotive applications. On the other hand, aluminium often does not display an endurance limit in fatigue, so failure eventually occurs even at rather low stresses. Because of its low melting temperature, aluminium does not perform well at elevated temperatures. Finally, aluminium alloys have allow hardness, leading to poor wear resistance. Designation: Aluminium alloy can be subdivided into two major groups, wrought and casting alloys, based on their method of fabrication. Wrought alloys, which are shaped by plastic deformation, have compositions and microstructures significantly different from casting alloys, reflecting the different requirements of the manufacturing process. Within each major group we can divide the alloys into two subgroups; heat treatable and nonheat treatable alloys. Heat treatable alloys are age hardened, whereas nonheat treatable alloys are strengthened By solid solution strengthening, strain hardening, or dispersion strengthening. Aluminium alloys are designated by the numbering system in Table. 1. The first number is specifics the principle alloying elements and the remaining numbers refer to the specific composition of the alloy. Table 1. Designation system of aluminium alloys. The degree of strengthening is given by the temper designation T or H. depending on whether the alloy is heat treated or strain hardened (Table 2.). Other designations indicate if the alloy is annealed (O). solution treated (W), or used in the as-fabricated condition (F). The numbers following the T or H indicate the amount of strain hardening, the exact type of heat treatment, or other special aspects of the processing of the alloy. Table 2. Temper designations for aluminium alloys F As-fabricated (hoi worked, forged, cast, etc.) O Annealed (in the softest possible condition) H Cold worked Hlx - told worked onh. (x refers t<» the amount of mid wo, \ ;ıwl sueııgılıeıım;.;.) H12 - gives a tensile strength midway between the O ~nd H14 tempers. Hİ4 - gives a tensile strength midway between the O and HIS tempers. H16 - gives a tensile strength midway between the HI4 and H18 tempers. H 1JŞ - gives about 75 /? reduction. H19 - gives a tensile strength greater than "000 »si of that obtained by H18 temper. H2x - cold worked and partly annealed. H3x - cold worked and stabilized at a low temperature to prevent age hardening. W Solution treated T Age hardened Tl - cooled from the fabricatirn temperature and naturally aged. T2 - cooled from the fabrication temperature, cold worked, and naturally aged. T3 - solution treated, cold worked, and naturally aged. T4 - solution treated and naturally aged. T5 - cooled from the fabrication temperature and artificially aged. T(5 - solution treated and artificially aged. T7 - solution treated and stabilized by nveraginp. T8 - solution treated, cold worked, and artificially aged. T9 - solution treated, artificially aged, and cold worked. T10- cooled from the fabrication temperature, cold worked, and artificially aged. The movement of one solid surface over another is fundamentally important to the functioning of many kinds of mechanism, both artificial and natural. Surface deterioration is important in engineering practice. Its is often the major factor limiting the life and performance of machine components. Wear maybe defined as unintentional deterioration resulting from use or environment. It maybe considered essentially a surface phenomenon. The displacement and detachment of metallic particles from a metallic surface maybe caused by contact with another metal (adhesive or metallic wear), a metallic or a non metallic abrasive (abrasion) or moving liquids or gases (erosion). Wear is affected by a variety of conditions such as the type ol lubrication, loading, speed, temperature, materials, surface finish and hardness. In the wear cases, usually one type of damage is predominant. Abrasive wear occurs when hard particles slide or roll under pressure across a surface, or when a hard surface rubs across another surface. In abrasive wear, material is removed or displaced from a surface by hard particles, or sometimes by hard protuberances on a counterface, forced against and sliding along the surface. Several qualifying terms can be used in describing abrasion. A distinction is often made between two-body abrasive wear and three-body abrasive wear. Two- body wear is caused by hard protuberances on the counterface, while in three-body wear hard particles are free to roll and slide between two, perhaps dissimilar sliding surface. A drill bit cutting rock might experience two-body wear, while grit particles entrained between sliding surfaces, perhaps present as contaminant in lubricating oil, would cause three-body wear. Wear rates due to three-body abrasion are generally lower than those due to two-body abrasion, although the various mechanisms of material removal in the two cases differ only in relative importance rather than in nature. Adhesive wear is the most common type of wear. It contributes little to the occurrence of sudden failures. Adhesive wear occurs when one surface bonds to another with subsequent motion, rupture occurs in one of the materials. It takes place between two metals because ol sliding friction and wear pieces breaks from soft metal. If two metals have the some hardness, wear can occur on two surfaces and ii lubrication is perfect, adhesive wear will decrease. Although adhesive wear is the most common form of wear damage, abrasive wear is more dangerous. It may occur suddenly with the introduction of a contaminant. It produces high wear rates and catastrophic failure of a system. Pitting is the result of the fatigue failure of the surface metal. Repeated application of relatively low stresses may result in numerous pit-like cavities in the metal surface. The characteristics of surface fatigue damage are different from those of ordinary fatigue. Fretting is the most common form of corrosion-assisted wear. Fretting or fretting-corrosion is due to a slight oscillatory motion between two mating surfaces under load. It manifests itself as pits in the surface surrounded by oxidation debris. In this study the Metal-Metal and Metal-Abrasive wear behaviour ol Al-Si-Cu casting and Al-Mg-Si wrought alloys were investigated after hardening with various methods. Al-Si-Cu and Al-Mg-Si alloys were hardened by cold working, heat treatment (solution treatment+aging) and combination of cold working and heat treatment (solution treatment+cold work+aging). The following conclusions have been drawn from the investigations performed by hardened Al-Si-Cu and Al-Mg-Si alloys. 1-) From the conductivity measurements, it has been found that Al- Mg-Si alloy has better conductivity than Al-Si-Cu alloy. The conductivity of both alloys increased after ageing treatment. The best conductivity in the wrought Al-Mg-Si alloy has been obtained from the material which was solution treated, cold worked of 16% and aged(at 175°C for 16h). 2-) It has been observed that the hardness and the strength values ol both alloys were increased due to the solution treatment and ageing process. In addition the hardness and strength of 16% cold worked Al-Mg-Si specimens have been also increased. However, the hardness and strength values of these specimens which were solution treated. 16% cold worked and aged were observed to be a bit higher than those of conventionally aged alloys (solution treated and aged). 3-) It has been concluded from the Metal-Abrasive wear tests, that the ageing process for both alloys increased the abrasive wear resistance by a factor of 20%. The best abrasive wear resistance in wrought Al- Mg-Si alloys have been obtained from these specimens which were solution treated, cold worked and aged. This hardening procedure has also increased the wear resistance by a factor of 30% as compared with the original alloy. 4-) It has been found from the Metal-Metal wear tests, that the conventional ageing process increased the wear resistance by 10% ol both alloys. On the other hand the cold work process has also increased the wear resistance of the wrought Al-Mg-Si alloy. XIVHowever, the best wear resistance has been observed in solution treated, cold worked and aged specimens. In addition to conventional ageing process, application of cold working has been increased the wear resistance by 40%, compared with original wrought alloy. 5-) From the comparison of the weight loss of both alloys, it has been seen that Al-Si-Cu alloy has higher wear resistance than the Al-Mg-Si alloy.