Development of cast and heat treated 7075 alloy rifle receiver

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2015
Güngör, Ahmet Umur
Developing technology in the world makes products lighter and have higher strength values. That’s why, aluminum and titanium alloys start to be used instead of steel. It can be seen that 7075 aluminum alloy is one of the highest strength amongst the aluminum alloys. This alloy has a close tensile strength value to some steels, with help of the heat treatment applications and developing production technologies. Generally, industrial usage of 7075 alloy is machining of 7075 alloy extrusion slab into desired shape. However, it becomes costly and time wasting as making complicated and hollow products. Therefore, near net shape methods like thixoforming and squeeze casting are vital for these conditions. This work aimed to replace production method of rifle receiver part which is machined into a hollow structure from extruded T6 heat treated 7075 alloy slab which cause heavy raw material lost with casted and T6 heat treated preform which has close tensile properties and needs very little machining to turn into receiver part. In order to achieve this purpose, squeeze casting, thixoforming, sand casting, gravity die casting, SIMA and high pressure die casting experiments were conducted. In order to investigate mechanical properties of samples, tensile and hardness tests were performed. X-Ray Diffraction analysis (XRD) and Scanning Electron Microscopy analysis (SEM) were conducted to determine the intermetallics inside of samples after heat treatment. Moreover, average grain size of samples was obtained by optical microscopy technique. Newtonian thermal analysis method was used to compute solid fraction values with respect to temperature and time. Target mechanical values were determined as mechanical properties of extruded 7075-T6 alloy which are 150 HB hardness, 505 MPa yield strength and 11% elongation. Hardness target was reached after T6 heat treatment with squeeze casting method as 150 HB, die casting with vacuum support method as 160 HB and thixoforming method as 173 HB. Other methods could not reach the target hardness and has hardness values between 100 HB and 130 HB. 505 MPa yield strength target was achieved only by thixoforming method with 0.67 solid fraction as 526 MPa. Other close results were 429 MPa with squeeze casting method and 365 MPa with SIMA method. Elongation target was reached by semi-solid injection molding method as 11.5% but its other mechanical properties were poor. Elongation results of other methods were found to be between 4% and 5%.

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Citation Formats
A. U. Güngör, “Development of cast and heat treated 7075 alloy rifle receiver,” M.S. - Master of Science, Middle East Technical University, 2015.