The paper presents one of the most important mechanical properties of aluminium alloys used in the automotive industry, which mainly determine the material resistance to mechanical loads. Samples were made of aluminium alloys from the 3xxx series (core) and 4xxx series (clad). The latter material layer begins to melt at the brazing temperature (582°C) and forms brazed joints between the surfaces of the base sheets. Commonly, these alloys are used as aluminium brazing sheets and applied in automotive to heat exchangers manufacturing, i.e. radiators, condensers, evaporators, heaters, oil coolers and charge air coolers. Samples of these materials were subjected to mechanical property measurements. In order to assess the changes in the materials during their life cycle, the properties after the manufacturing process and the exploitation tests were compared. Therefore, brazing process was realized in N2 controlled atmosphere. Moreover, one of the most important investigations in terms of the heat exchangers working conditions simulation which is resistance to thermal shocks, was performed. The material working conditions indicate that they should comply with above test requirements, including liquid contact, whose temperature range may refer to 0÷90°C. Particular attention was focused on properties such as Martens hardness, Vickers hardness, Young`s modulus and plastic strain, which have significant role in evaluation of product performance and improving its lifetime. For the measurements, a Fischer Picodentor HM 500 nanoindenter equipped with a Vickers indenter was used. The main advantages of the nanoindentation technique are the accurate and reliable results which might optimize heat exchanger. Furthermore, an optical microscopy was applied to analyse the indentations on the sample surfaces.
Słowa kluczowe: aluminium alloys, automotive, heat exchanger, mechanical properties, Young modulus, nanoindentation.
Keywords: stopy aluminium, motoryzacja, wymienniki ciepła, właściwości mechaniczne, moduł Younga, nanoindentacja.
1. INTRODUCTION Aluminium alloys are commonly used in numerous fields of industry. The main advantages of their usage include: good thermal conductivity, low density, good specific strength (tensile strength divided by the density), adequate corrosion resistance, easy processes of machining and joining, ability to recycle and cost-effectiveness. Therefore, the automotive, which includes the heat exchangers division is one of the major users of aluminium alloys [1, 2]. Alloys from the aluminium-manganese and aluminum-silicon series, such as 3003, 3004, 3005, 3103, 3203 and 4045, 4047, 4343 have often been used in mentioned sector. The most popular solution for these materials, regarding brazing sheets, is a core alloy (3xxx series) rolled with a clad alloy (4xxx series). Thanks to the layered combination of these materials, brazed joints can be formed using several brazing techniques [3÷9]. Aluminium alloys used in the automotive industry should meet a number of quality requirements. The important ones are appropriate mechanical properties, such as hardness, plastic deformation, indentation creep, elastic modulus and fracture toughness. Thus, their analysis is significant in the product control stage [5, 10÷12]. Numerous publications about the mechanical properties of aluminium alloys used in the automotive sector of industry have been written in the last years. For example, Kahl et al.  presented the results of fatigue, tensile and creep properties of the above materials measured at different temperatures. Dubey  compared features such as reliability, performance, weight and cost-effectiveness of aluminium and copper alloys. Takagi et al.  discussed the effects of creep phenomenon of an aluminium- magnesium alloy using the microindentation technique. Further scientific papers correlated the residual strain with the hardness value by the nanoindentation method  while another presented evaluation of the elastic m [...]
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