Abstract
Magnesium alloys are highly strain rate sensitive and exhibit good workability in a narrow forging temperature range. Consequently, parts made of these materials are usually forged with low-speed hydraulic presses, using specially designed tool heating systems in order to ensure near-isothermal conditions. This study investigates whether popular magnesium alloys such as Mg-Al-Zn can be forged in forging machines equipped with high-speed forming tools. Experimental upset forging tests on AZ31B, AZ61A and AZ80A specimens were conducted, using a screw press with a ram speed of 0.5 m/s and a die forging hammer with a ram speed at stroke of about 5 m/s. Test specimens were preheated to 350 °C, 410 °C and 450 °C. After the upset forging process, they were air- or water-cooled and then examined for their workability, hardness and grain size. To validate the results, a forging process for a producing handle was designed and modelled by the finite element method. Distributions of strain, temperature and fracture criterion were analysed, and energy and force parameters of the forging process were calculated. After that, experimental tests were performed on AZ31B and AZ61A specimens in order to determine mechanical properties of forged parts and examine their micro- and macrostructure. Results have demonstrated that AZ80A is not suitable for forging with either the screw press or the die forging hammer, that AZ61A can be press- and hammer-forged but to a limited extent, and that AZ31B can be subjected to forging in both forging machines analysed in the study.
Highlights
Due to their low specific weight and high relative strength, magnesium alloys are used as cast or wrought alloys in many industries such as aviation and aerospace, automotive, sports and recreation, electronics, and medical [1,2,3]
The screw press model was defined by a ram speed of 0.5 m/s, while the die forging hammer model was described with a drop part weight of 1200 kg (1000 kg ram weight + 200 kg die weight), blow energy of 36 kJ and efficiency of 80%
The results of the AZ61A specimens show that this alloy retains satisfactory workability when subjected to screw press forging, with the specimens preheated to 410 ◦ C (Table 5)
Summary
Due to their low specific weight and high relative strength, magnesium alloys are used as cast or wrought alloys in many industries such as aviation and aerospace, automotive, sports and recreation, electronics, and medical [1,2,3]. Forging plants manufacturing parts made of magnesium alloys use hydraulic presses equipped with specially designed tool heating systems to ensure near-isothermal conditions. The limitation of this technology is its low efficiency and a high cost of tools provided with such heating systems, not to mention the fact that these factors significantly increase production costs. The scientific aim of this study is to determine the relationships between forging temperature and deformation speed related to forging machines as well as between cooling method and properties (workability, hardness and structure quality) of selected magnesium alloys subjected to forging with industrial forging machines such as screw presses and forging hammers. The main practical goal of the study is to develop the technological assumptions of a hot forging process for selected magnesium alloys, conducted with screw presses and forging hammers that are available in many standard forging plants
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