Question: What rifle is the basis for the the magazine-fed, gas-operated semi-automatic rifle designed to be manufactured with the extensive use of aluminum alloys and synthetic materials?

Context articles: MIL-DTL-5541
Akdal MKA 1919
Marlin Model 70P
Leader Dynamics Series T2 MK5
Colt AR-15
FN Model 1949
Retrogression heat treatment
MAS-49 rifle
Aluminium alloy
AR-15 (disambiguation)

The military specification referred to as MIL-DTL-5541, "Military Specification, Chemical Conversion Coatings on Aluminum and Aluminum Alloys" covers chemical conversion coatings formed by the reaction of chemical conversion materials with the surfaces of aluminum and aluminum alloys.
 The current specification (2009) is MIL-DTL-5541F, which superseded MIL-C-5541E in July 2006.
 The specification is approved for use by all departments and agencies of the United States Department of Defense (DoD).
 Although prepared specifically for DoD applications, the standard is used for many commercial applications as well.
 It has gained world wide use across many fields versus the more verbose ISO equivalent (i.e., ISO 8081:1985, Aerospace process, Chemical conversion coating for aluminum alloys, General purpose).
 Note that chromate conversion coatings have been used for over 50 years as treatment to coated or as-fabricated surfaces to boost corrosion resistance and provide a good basis for the subsequent application of paint.
 However, these treatments use hexavalent chromium chemicals that are extremely toxic.
 This has led to progressively greater restrictions, imposed by national and international legislation, related to concerns over health and safety and environmental protection, on the use of these treatments.
The Akdal MKA 1919 is a gas operated, semi-automatic shotgun that resembles the M16 rifle and mimics the layout and placement of some of the controls.
 It was created by Turkish company Akdal Arms.
 The MKA 1919 uses a conventional gas-operated action which is located around the support tube that runs below the barrel.
 The return spring is also located around the same support tube which is concealed by an enlarged polymer handguard.
 The MKA 1919 barrel can be quickly removed from upper receiver.
 To charge the rifle, the charging handle on the receiver must be pulled.
 The upper receiver is manufactured from an aluminum alloy while the lower receiver, along with pistol grip and shoulder stock, is manufactured as one piece from impact-resistant polymer.
 Akdal MKA 1919 semi-automatic rifle has a 5-round detachable box magazine.
 It has a bolt release identical in location and function to the one on the M16.
 Manual safety also duplicates M16-style being located on the left side of the receiver above the pistol grip.
 Standard sights include a front post installed on the M16-style removable base and a detachable M16A2-style carrying handle with built-in diopter sight.
 On the upper receiver, an integral Picatinny rail exists which will accept detachable carrying handle or optional red-dot or other optical sight attachments.
The Marlin Model 70P, also known as the Marlin Papoose, is a .22 Long Rifle semi-automatic rifle manufactured by Marlin Firearms.
 The rifle is notable for its portability; it is less than 21 in in length when disassembled and weighs 3.25 pounds.
 Disassembly requires loosening a barrel retention nut by hand or with a supplied tool.
 It is designed as a hiker and camper utility rifle, and appeals to the same market as the AR-7.
 The Model 70P is based on the earlier Marlin Model 70 (currently listed as Model 795) that has a fixed barrel and conventional stock.
 Its semi-automatic action originated with the Marlin Model 60.
 The Marlin Model 70PSS variant has a synthetic stock and stainless steel barrel.
The Leader T2 MK5 Series weapons were chambered for the 5.56×45mm NATO cartridge and manufactured by Leader Dynamics of Smithfield, NSW, Australia (1978-1982/1983).
 The Leader was the brainchild of weapons designer Charles St. George.
 It was originally a contender for a 5.56 mm Australian military service rifle to replace the then-issued Lithgow L1A1-F1 SLR and Colt M16A1 rifles.
 What was unique about this endeavor was that Australia had never designed or manufactured its own commercial gas-operated semi-automatic rifle.
 The rifle was abandoned when the Steyr AUG was adopted for use by the Australian military.
The Colt AR-15 is a lightweight, 5.56×45mm, magazine-fed, gas-operated semi-automatic rifle.
 It was designed to be manufactured with the extensive use of aluminum alloys and synthetic materials.
The Fabrique Nationale Model 1949 (often referred to as the FN-49, SAFN or AFN) is a rifle available as both a semi-automatic rifle and as a selective fire automatic rifle designed by Dieudonné Saive and manufactured by Fabrique Nationale.
 It was used by the militaries of Argentina, Belgium, the Belgian Congo, Brazil, Colombia, Egypt, Indonesia, Luxembourg, and Venezuela.
 The automatic rifle version with selective fire produced for Belgium was known as the AFN.
Retrogression heat treatment (RHT) is a heat treatment process that rapidly heat treats age-hardenable aluminum alloys. Mainly induction heating is used for RHT.
 In the past, it was mainly used for 6061 and 6063 aluminum alloys. Therefore, forming of complex shapes is possible, without creating damages like cracks.
 Even hard tempers (for example -T6) can be formed easily after subjecting these alloys to RHT.
The MAS-49 is a French semi-automatic rifle that replaced various bolt action rifles as the French service rifle that was produced from 1949.
 It was designed and manufactured by the government-owned MAS arms factory.
 The French Army formal designation of the MAS-49 is Fusil Semi-automatique de 7,5mm Modele 1949 ("semi-automatic rifle of 7.5mm model 1949").
 The MAS-49 semi-automatic rifle was produced in limited quantities (20,600 units), whereas the shorter and lighter variant, the MAS-49/56, was mass manufactured (275,240 units) and issued to all branches of the French military.
 Overall, the MAS-49 and 49/56 rifles gained the reputation of being accurate, reliable and easy to maintain in adverse environments.
 All the MAS-49 and 49/56 rifles feature a rail on the left side of their receivers to accommodate a designated rifle scope.
 The MAS-49 and MAS-49/56 were replaced as French service rifles by the FAMAS assault rifle in 1979.
Aluminium alloys (or aluminum alloys; see spelling differences) are alloys in which aluminium (Al) is the predominant metal.
 The typical alloying elements are copper, magnesium, manganese, silicon, tin and zinc.
 There are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories heat-treatable and non-heat-treatable.
 About 85% of aluminium is used for wrought products, for example rolled plate, foils and extrusions.
 Cast aluminium alloys yield cost-effective products due to the low melting point, although they generally have lower tensile strengths than wrought alloys.
 The most important cast aluminium alloy system is Al–Si, where the high levels of silicon (4.0–13%) contribute to give good casting characteristics.
 Aluminium alloys are widely used in engineering structures and components where light weight or corrosion resistance is required.
AR-15 most commonly refers to the Colt AR-15, a line of semi-automatic rifles manufactured by Colt, based on the United States military M16 rifle.