duralumin, Duran, duralumin?
The main alloying element in these alloys – duralumin – Copper is mainly the content of 3 to 6 %. Magnesium also serves as the basic alloying elements in a content of 0 to 2 %. High strength alloys provided by the particulate hardening. Alloys of this series have a very good fatigue performance.
This series includes a first aluminum alloy Thermally – dyuralyuminii – D1 GOST 4784. More durable alloy D16 formerly called superdyuralyuminom. Often all of the alloys in this series is called duralumin, duralumin or duralumin.
That alloy D1 and D16 produced most aluminum boats in Soviet times. Therefore, all aluminum boats – not necessarily because of duralumin alloy – still call “dyuralkamy”.
The role of copper in duralumin
The presence of copper, However, a bad effect on corrosion resistance of the alloys. Copper tends to precipitate at the grain boundaries, What makes these alloys are very susceptible to pitting, intergranular corrosion and stress corrosion. These copper-rich zones are found to be galvanically more noble (cathodic), than the surrounding aluminum matrix and are therefore particularly vulnerable to corrosion, which takes place on an electrochemical mechanism.
Moreover, Copper is very harmful for anodizing. Copper particles are dissolved in an acidic electrolyte the anode, leaving a hole in the oxide layer, and dissolved copper migrates under the electric field to the interface between the aluminum and its oxide, which has a negative influence on the quality of the anodic coating.
With the increase in copper content in the alloy up to 12 % its strength properties increased due to dispersion strengthening mechanism. Hardening is achieved by precipitation of intermetallic particles Al2With или Al2CuMg aging, that provides strength, second only to the strength of high-strength alloys of the 7xxx series. When the copper content is more 12 % the alloy becomes brittle.
The use of duralumin
Aluminum profiles from alloys with moderate copper content, such as regular 2024 and 2014 (D16 and AK8) are in demand by the automotive industry. Aluminum profiles of these alloys have quite a good machinability, spot weldability and good corrosion resistance (compared to profiles made of high copper content alloys).
Aluminum profiles 2xxx series alloys used in such structures responsible, as airplanes, military equipment, bridges, heavy trucks. The additive alloying elements with a low melting point, such as lead and bismuth, It allows automatic machining these alloys, which makes them suitable for application by weight products, such as screws, bolts, fasteners. Currently, due to environmental restrictions on the use of lead to him looking for a replacement for other fusible elements.
Alloy 2117 (D18) is specially designed for manufacturing aluminum rivets, which are widely used in aircraft, as well as in other areas, for example, when aluminum boat manufacturing and repair.
To improve thermal resistance aluminum profiles, enhance their workability and weldability, as well as improved castability in the casting of pillars may be administered manganese additives, vanadium, zirconium, titanium.
Manganese increases the strength properties of alloys Al-Cu–Mg, but reduces ductility, therefore its content is limited 1 %.
Iron is added to Al-Cu-Ni alloys to increase strength at elevated temperatures (for example, alloy 2618 - АК4). Iron contributes to grain refinement. In alloys without nickel iron content is limited, so it can reduce the strength of the alloy, if iron overload is not linked in the silicon particle α-Fe-Si. This excess iron forms compounds with copper and, Consequently, "Seeds" in copper alloy, which it needs for thermal bonding.
Nickel in an amount of 0,8 to 2,3 % increases the strength and hardness of the alloys Al-Cu–Mg at elevated temperatures. However all additives 0,5 % nickel simple duralumin Al–4%Cu–0,5%Mg (2017 - D1) reduce its strength at room temperature.
The chemical composition of duralumin
European Standard ET 573-3 It includes 17 2xxx series alloys and modifications thereof, GOST 4784-97 – 12.