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25 votes
Accepted

How can I tell if I got counterfeit aluminum?

I figured out a simple test. Since the density of 6061 is 2.5 g/cm3 and the density of zinc is over 7 g/cm3, all I had to do was measure the density of the material. This showed that indeed it was ...
Wallace Park's user avatar
  • 1,635
21 votes

Can titanium be used as I-beams?

Not to repeat, but in addition to being very expensive it is very expensive to work with. So, pretty much only governments can afford it. It absorbs oxygen and nitrogen from air at the hot ...
blacksmith37's user avatar
  • 6,154
19 votes

Can titanium be used as I-beams?

Yes, but titanium is very difficult to roll into structural shapes like I-beams in a rolling mill and extremely sensitive to chemical attack by washing solutions that contain chlorine, for example. So ...
niels nielsen's user avatar
17 votes

Copper is more conductive, so why use lead battery terminals?

Yes, copper is more conductive than lead, but that is not necessarily the primary criterion for selecting the connector material. For car batteries, making sure there's a good connection between the ...
Dave Tweed's user avatar
  • 6,894
15 votes
Accepted

Unknown metal-piece connected to the case of an iPod Nano 2

It's a naked piezoelectric buzzer. Some piezoelectric crystal grown on a metal circle are the active part and the bottom contact glued on the back cover. The top is then metallised to get the second ...
carloc's user avatar
  • 295
15 votes

Why does faster cooling produce smaller grains?

Grain boundaries cost energy—the bonding quality is worse there—so there's always a driving force to form one giant grain. However, slow kinetics limit this process, so we generally encounter only ...
Chemomechanics's user avatar
12 votes

What is the purpose of grid-like details on engine blocks?

This pattern is to provide sufficient strength while minimising the mass of the block. These "webs" are designed to prevent any vibration, if the block wall was made thin and the full length and ...
Solar Mike's user avatar
  • 15.9k
12 votes

Can titanium be used as I-beams?

Yes. Besides aerospace, titanium structural elements are fairly common in offshore oil and gas and chemical industries. You can order titanium I-beams online, with prices available at some websites. I'...
Therac's user avatar
  • 221
11 votes

Why does corrosion take place at certain stressed regions?

One of the mechanism that affect corrosion is known in the literature as Stress Corrosion Cracking (SCC). The idea is that tensile stressed regions are prone to crack development. Crack development ...
NMech's user avatar
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10 votes
Accepted

Galvanized Steel (Zinc Plated Steel) vs Stainless Steel

Stainless steel can be used up to temperatures of about 1000C. The corrosion resistance of zinc plating decreases rapidly above 100C, and embrittlement can occur above 500C. Zinc plating has lower ...
alephzero's user avatar
  • 12.5k
10 votes

How can I tell if I got counterfeit aluminum?

You can confirm the alloy and heat treating condition by measuring conductivity. It's like a fingerprint for any given combination of alloy composition and heat treatment. Reference values can be ...
haarigertroll's user avatar
9 votes

Copper is more conductive, so why use lead battery terminals?

A lead-acid battery has only lead and acid. If copper was used for the terminal posts galvanic corrosion would eat them. It is better to keep the same metal for the cell plates and the terminals. Also ...
ronald glen's user avatar
9 votes

Can titanium be used as I-beams?

Yes, Titanium can be used as a structural material (not necessarily I beam), though rare. Here are two structures made of titanium, Monument to Yuri Gagarin and Monument to the Conquerors of Space, ...
r13's user avatar
  • 8,202
7 votes
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Word for the tendency of one metal to rub off on another?

"Galling" is probably the word you want here. It's the tendency of a (usually) soft metal to break down under pressure and adhere to the harder material. It's common with soft metals like aluminium, ...
Andy's user avatar
  • 285
7 votes

Is there a maximum life for things made out of stainless steel or cast iron?

Strictly speaking, very few metals are "stable" in terms of the laws of thermodynamics. True chemical stability is when the atoms are in their lowest energy state. For most metallic elements,...
Brian Ensign's user avatar
7 votes

How can I tell if I got counterfeit aluminum?

Unlikely you have anything except aluminum alloy. What is the heat treatment supposed to be ; what grades are offered in the spec? On the net, I see reference to T-5, that is- as extruded, then aged; ...
blacksmith37's user avatar
  • 6,154
6 votes
Accepted

Why are vacancies in solids called as equilibrium defects?

Imagine you have two boxes separated by a removable partition. Each box is filled with a different pure monatomic gas. When you remove the partition, the gases mix. Their equilibrium state tends ...
do-the-thing-please's user avatar
5 votes

Copper is more conductive, so why use lead battery terminals?

Lead is more corrosion resistant to sulfuric acid . And copper is more expensive. That is; copper in the battery would dissolve in less than one year.
blacksmith37's user avatar
  • 6,154
4 votes

How can the alloying materials of recycled steels be separated?

First the scrap is separated at the source ; for example cast iron generally only contains Si and Mn. High vapor pressure elements boil off or collected in the flux/slag : eg, Zn, Pb, Sn, Bi, An ,,,,...
blacksmith37's user avatar
  • 6,154
4 votes

What is the purpose of grid-like details on engine blocks?

As mentioned in other answers these patterns are structural stiffeners to give strength to a lighter engine block. But they also have the task of distributing stresses due to internal vibrations of ...
kamran's user avatar
  • 22.5k
4 votes
Accepted

Purpose of a GD-Zn alloy

When I look on the net I found a surprising result : GD seems to stand for German Din (material specifications). GD Zinc is a zinc die cast alloy with 4 Cu and 1 Al. Equivalent to AG 41A alloy in the ...
blacksmith37's user avatar
  • 6,154
4 votes

Why do you need helicoil if you can just use a tap?

The threads made by the tapper used for helicoil is not going to work with the standard size bolts. The taps used are specific STI (Screw Thread Insert) tools. But of course, if you decide the old ...
kamran's user avatar
  • 22.5k
4 votes

Why do you need helicoil if you can just use a tap?

Why does the helicoil need to be inserted if you have already tapped the new threads into a hole? Can't you just put a bolt in once you've tapped new threads? Consider the case of an M5 x 0.8 tapped ...
Transistor's user avatar
  • 10.9k
4 votes

Is it possible to determine how the steel was made, having its microstructure (for example, to distinguish forging from rolled products)?

Steels are usually considered "as cast" or wrought. The microphotograph is overetched and either high magnification or coarse grained , likely had a heat-treatment. Cast or wrought would be ...
blacksmith37's user avatar
  • 6,154
4 votes
Accepted

Why does corrosion take place at certain stressed regions?

In the real world ,I don't believe I have seen CORROSION at STRESSED areas. Corrosion may be accelerated at STRAINED areas; the strains introduce energy to the microstructure which may promote ...
blacksmith37's user avatar
  • 6,154
4 votes

Can Rotary Friction Welding be used to join metals and ceramics?

Probably not. The friction welding process presupposes a certain level of ductility so the mating surfaces can deform together and completely bond. Ceramics lack the deformation mechanisms that metals ...
niels nielsen's user avatar
4 votes

What is the characterising difference between a riser and a runner?

A riser is a static reserve volume of metal available to flow into the casting to compensate for shrinkage as the liquid freezes. Risers are relatively large because they should not freeze until after ...
blacksmith37's user avatar
  • 6,154
4 votes
Accepted

What does time temperature specifically give us?

You left off a "T" ; it is "time, temperature, transformation". It is a basis to evaluate hardenability of alloy steels. A sample is austenitized, then rapidly cooled to some ...
blacksmith37's user avatar
  • 6,154
4 votes

How the choice of etchant can affect the severity of hydrogen embrittlement during pickling and passivation?

The primary cause of hydrogen cracking is a susceptible matrix . Typically a carbon or low alloy steel that is hard ( > HRC 25) untempered is the primary problem. The martensitic chrome steels were ...
blacksmith37's user avatar
  • 6,154
3 votes

Copper is more conductive, so why use lead battery terminals?

In regular wet lead batteries, the corrosive environment and the need to have easy connect and disconnect ensures there will be an oxide film at the connection due to the sulphuric acid fumes. While ...
Phil Sweet's user avatar
  • 4,765

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